Soils Under Stress: Nutrient Recycling and Agricultural Sustainability in the Red River Delta of Northern Vietnam

edited by Aran Patanothai

February 1996

East-West Center

Program on Environment

Center for Natural Resources Management

and Environmental Studies, Hanoi University

Southeast Asian Universities

Agroecosystem Network

E A S T - W E S T C E N T E R Soils Under Stress:

Nutrient Recycling and

Agricultural Sustainability

in the Red River Delta

of Northern Vietnam

edited by Aran Patanothai

February 1996

A joint research activity of

• East-West Center

Program on Environment

• Center for Natural Resources

Management and Environmental

Studies, Hanoi University

• Southeast Asian Universities

Agroecosystem Network

• University of Hawaii

• Hanoi Agricultural University

About the V o l u m e E d i t o r

D r . A r a n P a t a n o t h a i is an associate professor and dean of the Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand. He is also the secretariat of the Southeast Asian Universities Agroecosystem Network (SUAN) and the coordinator of the SUAN Sustainable Land Use Task Group. He spent eight months from February to September 1992 at the East-West Center as a research scholar, at which time he led the team in conducting this research.

LIBRARY OF C O N G R E S S C A T A L O G I N G - I N - P U B L I C A T I O N DATA

Soils Under Stress: Nutrient Recycling and Agricultural Sustainability in the Red River Delta of Northern Vietnam,

p. cm. "February 1996."

"A joint research activity of the Southeast Asian Universities Agroecosystem Network, the Program on Environment of the East-West Center, the University of Hawaii, the Center for Natural Resources Management and Environmental Studies of Hanoi University, and the Hanoi Agricultural University."

Includes bibliographical references. ISBN 0-86638-180-5 i. Agriculture—Vietnam—NguySn Xa. 2. Land use, Rural—

Vietnam—Nguyen Xa. 3. Agricultural productivity—Vietnam— Nguyen Xa. 4. Sustainable development—Vietnam—Nguyen Xa. 1. Patanothai, Aran. n. Southeast Asian Universities Agroecosystem Network.

S471.V475N485 1996 338.r'4,09597—dc20 96-1721

To secure copies, write to the

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© 1996 by East-West Center. All rights reserved. Printed in the United States of America.

Figures and Tables v

Foreword ix

Acknowledgments xm

Background of Report xv by A r a n P a t a n o t h a i

Chapter i A n Overview of the Red River Delta and Nguyen Xa Village i

by A r a n P a t a n o t h a i

Chapter 2 Evolution of Agricultural Production and Resource Management 19

by N g u y e n V a n H o a n , H a r o l d /. M c A r t h u r j r . , G o r o U e h a r a , a n d Vy T o n

Chapter 3 Soil Characteristics and Changes in Their Chemical Properties 31

by D a o C h a u T h u , Russell S. Yost, R o j a r e e N e t s a n g t i p , K e i t h F a h r n e y , a n d A r a n P a t a n o t h a i

Chapter 4 Contribution of Sediment to Nutrient Flow 43

by T r a n D a n h T h i n a n d G o r o U e h a r a

Chapter 5 Azolla Production 47 by P h a m T i e n D u n g , N g h i e m P h u o n g T u y e n , a n d A r a n P a t a n o t h a i

iv Soils Under Stress

Chapter 6 Nutrient Balances in Relation to Land-Use Sustainability 51

by A r a n P a t a n o t h a i a n d Russell S. Yost

Chapter 7 Subsidiary Enterprises and Their Effects on Agricultural Production 83

by L e T r o n g C u e , T r a n D u e V i e n , a n d P h a m V a n Phe

Chapter 8 Potential for Further Increase in Agricultural Production 91

by G o r o U e h a r a a n d A r a n P a t a n o t h a i

Chapter 9 Land-Use Sustainability 97 by A r a n P a t a n o t h a i

Appendices A . Workshop Participants 105 B. Workshop Schedule 107 C. Questionnaire 109

References 119

FIGURES ANDTABLES

Figures

1.1 Vietnam and the Red River Delta 2

1.2 Hydrological and dike system of Thai Binh Province 5

1.3 Cross-section of Nguyen Xa landscape 14

1.4 Canal and dike system of Nguyen Xa 18

5.1 Percent of paddy area with azolla cultivation in

Nguyen Xa 48

6.1 Hypothetical input-output model of Nguyen Xa 53

6.2 Nutrient flows among village subsystems and between village and outside systems 55

6.3 Nutrient flows between double-cropped rice fields, households, and other subsystems—spring and fall 58

6.4 Nutrient flows for double-cropped rice fields 75

6.5 Nutrient flows for triple-cropped fields 75

Tables

I .I Nguyen Xa land use 13

2.1 Chronology of events and agricultural changes 20

2.2 Rice varieties and cropping calendar during key phases of agricultural developmcntiri Nguyen Xa 28

3.1 Results of soil analysis of samples taken during the field study in 1992 34

vi Soils Under Stress

3.2 Soil chemical properties of Nguyen Xa and their relationship with land topography and depth of plow pan|i992) 36

3.3 Changes in chemical properties of Nguyen Xa soils during 1985-92 37

3.4 Distribution of fields in which p H class changed during 1985-92 38

3.5 Distribution of fields in which organic matter class changed during 1985-92 38

3.6 Distribution of fields in which available phosphorus class changed during 1985-92 39

6.1 Distribution of family size and farm laborers 59

6.2 Distribution of number of fields per household 59

6.3 Frequency distribution of households with different

number of pigs 60

6.4 Amount of pig manure and night soil produced by individual households in 1991 60

6.5 Amount of buffalo manure produced by individual households in 1991 61

6.6 Correlation coefficients between pig manure, night soil, and buffalo manure produced and certain characteristics of households 61

6.7 Use of pig manure and night soil 62

6.8 Characteristics of the fields grown to different cropping patterns 64

6.9 Distribution of good, moderately good, and poor fields in the different land topography and land classes 65

6.10 Distribution of fields with different land topography in different land classes 65

6.11 Means of input and crop yield for different cropping patterns (1991) 66

Figures and Tables vii

6.12 Distribution of fields at different rates of fertilizer application for rice and winter crops 67

6.13 Means of input and crop yield for different soil fertility classes 69

6.14 Means of input and crop yield for different land classes 71

6.15 Means for minimum, actual {in 1991}, and maximum yields of different crops 72

6.16 Distribution of fields at different yield levels for individual crops 73

6.17 Means for input, output, and balance of nutrient elements for different cropping patterns 76

6.18 Distribution of fields with different levels of nutrient balances 79

6.19 Total balances of nutrient elements at minimum, actual, and maximum yield levels for the different cropping patterns 80

A6.1 Nutrient concentration of outflow and inflow components 82

7.1 Income from different sources of five selected households in Nguyen Xa 86

8.1 Comparison of observed and predicted heading date, maturity date, and grain yields for the 1982-90 spring rice crops transplanted on 15 February (day 46) 94

8.2 Comparison of observed and predicted heading date, maturity date, and grain yields for the 1982-91 autumn rice crops transplanted on' 15 July (day 197) 94

FOREWORD

Since 1989 the Program on Environment of the East-West Center (EWC) and the Center for Natural Resources and En­vironmental Studies (CRES) of Vietnam National University (formerly Hanoi University), Hanoi, have been collaborating on a long-term research and training project on human ecol­ogy in Vietnam. The goals of this project are to increase un­derstanding of human interactions with the environment as a basis for developing more sustainable approaches to man­agement of rural ecosystems and conservation of biodiver­sity and to enhance the capacity of Vietnamese scientists to conduct applied environmental research. Over the years this project has received funding from the Ford Foundation, the Rockefeller Brothers Fund, and the John D. and Catherine T. MacArthur Foundation.

As part of this project we have carried out a series of field studies of critical ecosystems in various regions of Viet­nam. Most of these studies have been in the midlands (Le Trong Cue, Gillogly, and Rambo 1990; Le Trong Cue et al., 1996) and mountains (Rambo 1995) where environmental degradation is most evident and natural biodiversity clearly most threatened (Rambo et al. 1995). In 1991, however, we turned our attention to the Red River Delta, Vietnam's most populous and intensively cultivated region, and the focus of the French tropical geographer Pierre Gourou's pioneering work (1936} on Vietnamese human ecology. With some 13 mill ion people on a surface area of less than 20,000 km 2 , the Red River Delta supports about 900 persons/km 2 (2,340 per­sons/mi2), making it one of Asia's most densely populated areas. The landscape is wholly dominated by people and their works with almost no remaining wild species. Human de­mands on the environment are immense, making the ques­tion of the sustainability of the agricultural system of more than academic concern.

x Soils Under Stress

With funding provided by a grant to the E W C by the John D. and Catherine T. MacArthur Foundation, and draw­ing on the help of scientists from the Southeast Asian U n i ­versities Agroecosystem Network (SUAN), CRES and the EWC organized a preliminary study of the human ecology of Nguyen Xa Village in Thai Binh Province. Nguyen Xa was chosen for this study because, with a people-to-land ratio of just under 1,500 persons/km 2, it is the most densely popu­lated village in the most densely populated province in Viet­nam. The findings of that exploratory study are reported in the monograph T o o M a n y P e o p l e , T o o L i t t l e L a n d (Le Trong Cue and Rambo 1993).

The exploratory study found that the farmers of Nguyen Xa were successfully producing enough food to meet their subsistence needs and even a small surplus to sell, despite the fact that they only had 490 m 2 of cultivated land per per­son. By that measure my suburban houselot in Honolulu, a city not noted for the spaciousness of its residential plots, would have to produce sufficient food to support three people if it were transported to Nguyen Xa. The farmers of Nguyen Xa carry out this near miracle of achieving food self-suffi­ciency on such a limited land area by producing incredibly high yields. On average, they reap n to 12 tons of paddy per hectare each year. These yields represent 80 percent of what the rice varieties they are planting are genetically capable of yielding under absolutely optimum conditions. For farmers working in a far-from-optimum real-world environment to obtain four-fifths of the genetically possible yield is an enor­mous accomplishment. Certainly there is no "yield gap" here offering the hope of major increases in productivity if con­straints can be overcome by improved technology.

The farmers achieve these high yields by a cultivation system of almost military precision, using locally adapted high-yielding varieties, carefully controlling irrigation wa­ter, and, above all else, by making heroic efforts to maintain the fertility of the soil. In our preliminary study in 1.991 Dr. Aran Patanothai led the team that focused on soil manage­ment. According to his team's findings (Chapter 10 in Le

Foreword xi

Trong Cue and Rambo 1993), the Nguyen Xa farmers appeared to be pushing the limits of sustainable land use. Because the future welfare of the Red River Delta's population so depends on the functioning of agroecosystems similar to that in Nguyen Xa, it seemed a priority to make a more intensive investigation of these soils under stress.

In 1992, therefore, Dr. Aran and a team of scientists from EWC, CRES, Hanoi Agricultural University, Chiang Mai University, and the University of Hawaii returned to Nguyen Xa to carry out a more in-depth study focused on the soil component of the Nguyen Xa agroecosystem. Their objec­tive was to do a careful input-output analysis of nutrients to determine if existing practices of land use were sustainable in the long term. The findings of their study are described in detail in the present monograph. They give cause for both hope and concern. Hope because the farmers have been suc­cessful so far in maintaining the fertility of the hard-worked soil while actually increasing the amount of food available per person, concern because current cultivation practices appear to threaten the sustainability of the soil component of the agroecosystem.

Despite their best efforts to maintain soil fertility, the farmers of Nguyen Xa are acidifying the soils of their pad­dies, thus making phosphorus less available to the rice plants, and also depleting potassium faster than it is being replaced. These changes in soil quality may result in declining yields over the long term. At the same time that the sustainability of the soil is threatened, continued population growth threat­ens to outstrip the ability of even the best-managed agro­ecosystem to meet minimal subsistence requirements. As Dr. Aran's study demonstrates, there is virtually no margin for improvement in yields; yet the number of mouths to feed is increasing by more than 1.5 percent per year. If the people of Nguyen Xa arc not to find themselves unwillingly vali­dating the prophecies of Malthus, they must find an alterna­tive to exclusive reliance on wet rice cultivation, such as raising high-value cash crops, operating side-line industries, and obtaining non-farm and off-farm employment, that w i l l

xii Soils Under Stress

generate income needed by households to purchase supple­mentary food. This is, as Dr. Aran reports, a search that the farmers themselves are already pursuing intently.

In addition to its detailed analysis of land-use sustain­ability, Dr. Aran's study offers valuable insights into the knowledge and behavior of the farmers of Nguyen Xa. It is their ski l l , tenacity, and resilience that have allowed them to survive in a difficult environment for many centuries. Their patiently acquired knowledge of how to successfully farm in that environment represents an immensely valuable scien­tific resource, one that has been used to maximum advan­tage by Dr. Aran and his colleagues. This study can be seen as a model for incorporating indigenous knowledge into rig­orous scientific research.

Finally, this monograph reveals the extent to which useful findings can be produced in a very short time by an interdisciplinary and multinational research team. Organiz­ing a field study involving scientists from three countries, five institutions, and a dozen disciplines is no simple mat­ter, however. Dr. Aran and his colleagues deserve no little credit for having successfully carried this project through to completion. The present report would seem to offer more than adequate justification for all their effort. It should be of interest not just to agronomists and soil scientists but to ev­eryone concerned with problems of rural development in Southeast Asia.

A . Terry Rambo, Director Program on Environment East-West Center

ACKNOWLEDGMENTS

We thank Mrs. Dao Thi Nhat, vice-chair of the People's Com­mittee of Thai Binh Province; Mr. Pham Quy Nhan, chair of the Committee of Science of Thai Binh; Mr. Tran Anh Thu, vice-chair of the People's Committee of Dong Hung District; Mr. Nguyen Xuan Phuoc, chair of the People's Committee of Nguyen Xa Village; and particularly Mr. Nguyen Van Chu, director of the Cooperative, for their help in arranging the field research and for giving us valuable information. Several villagers guided us to households and fields in different parts of the village. The government of Nguyen Xa was also very helpful to us. Most especially, we thank the farmers of Nguyen Xa for their warm hospitality and for patiently an­swering our questions.

Dr. Vo Quy, director of the Center for Natural Resources Management and Environmental Studies (CRES), Hanoi Un i ­versity (now the Center for Natural Resources and Environ­mental Studies, Vietnam National University, Hanoi), and personnel from CRES did their usual phenomenal job in or­ganizing the field research workshop. They obtained permis­sion for research, arranged for comfortable accommodations, transportation, and other logistical support, and also actively participated in the research. We thank them.

Funding for this research was provided by a grant to the East-West Center (EWC) from the John D. and Catherine T. M a c A r t h u r Foundat ion. The support is gratefully acknowledged.

Dr. A . Terry Rambo, director of the EWC Program on Environment (ENV), was the major driving force for this re­search. He allocated the funds, gave guidelines and technical advice, and provided all the necessary support. Administra­tive and logistical arrangements for the workshop were the responsibility of Ms. June Kuramoto of the E N V Program Office and Ms. Maureen Murakami of the E N V Fiscal Office.

xiv Soils Under Stress

Ms. Marilyn L i , E N V project assistant, ensured that necessary documents reached the proper people in a timely manner.

Initial draft reports of Chapters 2-8 were prepared by the individual research teams. These drafts were then com­bined and edited by Aran Patanothai, who also prepared the introductory chapter and the conclusion. Russell S. Yost, Goro Uehara, A . Terry Rambo, David Thomas, and Peter Pirie re­viewed the draft of the manuscript and made many useful suggestions for revision. Vivian Gutierrez, Christine Shiraki, and LisaNhomi assisted in the input of revisions to the manu­script. Final editing was done by Mrs. Helen Takeuchi, E N V senior editor. Editorial assistant Daniel Bauer produced the report.

Aran Patanothai

Background of Report

This report is the product of a joint research activity of the Southeast Asian Universi t ies Agroecosystem Ne twork (SUAN], the Program on Environment (ENV) of the East-West Center (EWC), the University of Hawaii (UH), the Center for Natural Resources Management and Environmental Studies (CRES) of Hanoi University, and the Hanoi Agricultural Un i ­versity (HAU). Data collection was organized as a research workshop held in Hanoi and Thai Binh Province from n to 30 June 1992. Participating in the research were fifteen re­searchers from Thailand, Vietnam, and the United States (see Appendix A for list of participants). Aran Patanothai of Khon Kaen University, coordinator of the S U A N Sustainable Land Use Task Group, and Le Trong Cue, deputy director of CRES, served as workshop coordinators.

CONCEPTUAL Conceptually, sustainability of land productivity was defined FRAMEWORK as the ability of the land to support a high and relatively stable

level of production over an extended period. This definition recognizes the necessity to increase production to meet the increasing demand for products of an increasing population, as well as the need to maintain or even improve the land quality to sustain a high level of production. These two goals are often conflicting; therefore, a trade-off has to be consid­ered in determining a management strategy.

To determine the long-term sustainability of land pro­ductivity, the nutrient balance was assessed by using an in­put-output model. Because long-term data were unavailable in most situations, this approach was considered logical and useful since it allows for identifying important input and

xvi Soils Under Stress

output variables for a specific situation. These variables can then be examined individually for their long-term effects and possibility of changes that might occur or could be induced. In fact, the main purpose of sustainability assessment is not the prediction of how l o n g the productivity w i l l last, but the identification of factors that are the likely causes of unsustain-ability so that ways to minimize their negative effects could be examined.

The basic concepts underlying these analyses are the concepts of human ecology, particularly the "system model of human ecology" (Rambo 1983), and agroecosystem analy­sis (Conway 1984), which have been used extensively by S U A N researchers. These concepts were described in detail in Le Trong Cue, Gillogly, and Rambo (1990) and also briefly reviewed in Le Trong Cue and Rambo (1993).

RESEARCH

METHODOLOGY

AND ACTIVITIES

A n excellent background information of Nguyen Xa Village has been published in Le Trong Cue and Rambo (1993). In the present study, additional data considered relevant to the objectives were collected. Data collection was organized as a research workshop held in Hanoi and Thai Binh, from 11 to 30 June 1992. Before the workshop, some secondary data had been collected by Vietnamese researchers, and related chap­ters of the draft report of the 1991 workshop (Le Trong Cue and Rambo 1993) were provided to the participants. The workshop began with a meeting in Hanoi to discuss the ob­jectives and field research activities, and to examine the pre­viously collected data. The participants then spent fourteen days in the field in Nguyen Xa and concluded with a meeting in Hanoi (see Appendix B).

The research methodology consisted of a formal sur­vey with a two-part questionnaire and rapid rural appraisal (RRA) techniques (Khon Kaen University 1987), including collection of secondary data, a semi-structured interview of households and key informants, direct observation, and di­rect measurement. The questionnaire was designed prima­rily to obtain quantitative data on input and output of the

Background of Report xvii

individual fields and on the land and labor resources of the households who manage the fields. The informal survey fo­cused on historical profiles and key events that influence the evolution of agricultural production and resource man­agement in the village, characteristics of the soils and land resource, land use and management, water management and sedimentation, crop and crop residue management, azolla production and its use, agricultural technology delivery sys­tem, and subsidiary enterprises and their effects on agricul­tural production. Small teams were formed to gather these data. During field research, meetings were held periodically, usually at night, to share information obtained among the individual teams. Water was sampled to determine sediment concentration, and soil samples were taken from selected spots to determine the acidity level and nutrient concen­tration. Computer input of data was also done during field research.

Subsequent data analyses were done at the East-West Center and the University of Hawaii. The analyses were con­centrated on estimating balances of nutrient elements in the dominant cropping systems and examining the relationships among the various input, output, and soil parameters. A geo­graphic information system was used in analyzing the spa­tial relationships, and the potential yield of rice crop was estimated by system simulation.

REPORT This report is organized into nine chapters. Chapter i gives ORGANIZATION a n overview of the physical and social environments of the

Red River Delta and Nguyen Xa and the use of the village land resource. Chapter 2 outlines the key historical events that have influenced the evolution of agricultural produc­tion and resource management in Nguyen Xa. Chapter 3 pro­vides more detail on the soil characteristics and changes in their chemical properties during the past seven years. Chap­ter 4 assesses the contribution of sediment to nutrient flow into the village. Chapter 5 examines the future prospect of azolla production. Chapter 6 presents the nutrient balance

xviii Soils Under Stress

analysis and speculates on the consequences of nutrients on land-use sustainability. Chapter 7 investigates the effects of subsidiary enterprises on agricultural production. Chapter 8 estimates the potential for further increase in agricultural production. The final chapter (Chapter 9) ends the report with an overall synthesis and conclusion regarding land-use sus­tainability of the area and prospects for future development.

C H A P T E R 1

Aran Patanothai

An Overview of the Red River Delta and Nguyen Xa Village

Sustainability of land productivity is a consequence of how the land is used and managed. Land use and management, in turn, is a complex decision, depending not only on the natu­ral environments but also on the social and economic forces impinged upon the local inhabitants. Thus, land-use sustain? ability is a result of complex processes driven by interacting factors prevailing in the area, including physical environment, climatic conditions, population growth, commercialization and trade, production technologies, land tenure, and alterna­tive opportunities. This chapter, extracted from an earlier report (Le Trong Cue and Rambo 1993), presents an over­view of the conditions in the Red River Delta and Nguyen Xa Village as a background to understanding the village land use and management.

THE RED RIVER PHYSICAL ENVIRONMENT

DELTA

The Red River Delta of north Vietnam in which the study site is located encompasses a total area of 17,321 km2. The area resembles a triangle .with Viet Tri at the top and the coastline of the Gulf of Tonkin stretching from Hai Phong to Ninh Binh at.the bottom, embracing sixprovinces: Hanoi, Hai Phong, Ha Nam Ninh, Ha Son Binh, Hai Hung, and Thai Binh (see Figure I.I). The area is inhabited by more than 13 million people and is one of the most densely settled rural areas in Asia. Population densities range from a low of 317 persons/km2 in Ha Son Binh to a high of 1,065 persons/km2

in Thai Binh, with an average of about 900 persons/km2.

2 Soils Under Stress

Thai Binh

Nguyen Xa Village

m & Ho Ch i M i n h City

Figure I.I Vietnam and the Red River Delta (Adapted from Le Trong Cue and Rambo 1993, 3)

Topographically, the Red River Delta can be divided into three sections: the low hills and mountains alternating with valleys at the fringes, the flat alluvial plain at the center, and the coastal area along the Gulf of Tonkin. The hills and moun­tains section is a slightly elevated area with maximum alti­tude not exceeding 10 m above sea level and average inclina­tion of 18° to 22°. The hi l l soils are fertile but concretion occurs in some places. The hi l l surface areas, however, are now seriously eroded and barren. The flat alluvial plain oc­cupies the largest area, with elevation ranging from 3 to 5 m above sea level. It is an ancient and stable part of the delta. This part formerly experienced alluvial deposition, but the large low-lying area is now interlaced by dike systems, and natural alluvial deposition no longer takes place. The coastal part has the youngest alluvial soils in the Red River Delta. The area is very flat and currently experiencing alluvial de­posit and sea encroachment.

The climate of the Red River Delta is tropical mon­soon, influenced by the ocean climate. Total average yearly rainfall is 1,600-1,800 mm. There are two distinct seasons: dry and rainy. The rainy season is from Apri l to October with

Overview 3

80-100 rainy days providing 80-8 5 percent of the yearly rain­fall. The highest rainfall [300-350 mm) occurs in August. Six to eight typhoons are normally generated during the rainy season, which can cause flooding in the delta area. The dry season is from November to March with forty rainy days pro­viding less than 150 mm of rainfall. The lowest rainfall (8-20 mm) occurs in December and January. The potential evapo­ration is between 900 and 1,000 mm/yr. Average humidity is 82-88 percent. During February and March, the northeast and southeast monsoons bring moisture from the ocean, caus­ing mists and drizzle and making this period the wettest in the year.

Total average radiation is 120 kcal/cm2/yr. The highest radiation takes place from May to December (12-14 kcal/ cm2/mo), whereas the lowest radiation occurs between Janu­ary and March (3.5-6.5 kcal/cm2/mo). The yearly average tem­perature is 230 C , with the maximum of 400 C and the mini­mum of 50 C. For about 90-100 days, the temperature is be­low 200 C, which favors temperate crops and facilitates the growth of winter crops. Average temperature in excess of 280

C ranges from 30 to 90 days from June to August. Total sunny hours are 1,640 hr/yr. Sunny hours during the winter crop-growing season are about 23-25 percent of the total.

The hydrology of the Red River Delta is dominated by the Red River system and the Thai Binh River system. The Red River's flow is high and carries a large amount of rich alluvial. The flow is 120 billion m 3 of water per year on the average, with a peak volume of 158 billion m 3 of water per year. In the flood season (from June to October), the river carries 73 percent of its total capacity (21 percent in August). In March, the volume is a low 2.6 percent. Its alluvial con­tent averages 1.31 kg/m3, 3-3.5 kg/nv1 in the flood.season, and 0.5 kg/m3 in the dry season.

The Thai Binh River's capacity and alluvial amount are lower than those of the Red River. The alluvial content con­tains a moderate amount of phosphorus, and its potassium content is much lower than that of the Red River. For this reason the soil deposited by the Thai Binh River system is

4 Soils Under Stress

more acid and less fertile than soil in other parts of the Red River system.

Flooding is the most dramatic hazard in the Red River system. In the past, there had been several incidents of se­vere floodings, some of which had caused extensive damage to properties and claimed the lives of delta inhabitants. Dur­ing reclamation and protection of the land, the people of the Red River Delta constructed an extensive dike system to control water. Generation by generation, the inland dike sys­tem and the coastal dike system developed to its current length of 7,764 km and 2,048 km, respectively (see Figure 1.2 for the dike system of Thai Binh). These systems culminated in maximum control against the threat of flooding. How­ever, since construction of the closed dike system, the delta has been isolated from the natural deposition and extension of the Red River system. Furthermore, due to the heavy sedi­ment load carried by the Red River, there is continuing aggra­dation of its channel so that today the level of the river dur­ing the rainy season is several meters higher than the sur­rounding plains. Despite continuous efforts by the govern­ment to maintain and strengthen the dikes, the threat of flood­ing remains real.

RURAL SOCIETY IN THE DELTA

Although the Red River Delta encompasses just a little over 5 percent of Vietnam's total natural area, its population is 21 percent of the country's total. The census taken in 1989 showed a delta population of 13.6 million. More than 83 per­cent live in rural areas. The average density in the lowlands of the Red River Delta is 923 persons/km2. From 1987 to 1990, the average growth rate was 1.4 percent per year.

The villages in the delta are clustered on elevated land, interspersed among low-lying fields. Under feudalism, the village was the fundamental social unit of the government and Was based on traditional institutions, regulations, and customs. It had relatively high autonomy in administration and economy. Two social classes existed in the village: the

Overview 5

River fm» j

River Dike —

Coastal Dike ^mm

Water Gate O

Figure 1.2 Hydrological and dike system of Thai Binh Province (Source: Le Trong Cue and Rambo 1993, 133)

upper class, who controlled and managed all activities in the village; and the lower class, the main labor force, who con­stituted the majority of the population.

The present-day political structure of the village is a var­iation of the traditional forms. The village is under the paral­lel leadership of representatives of three organizations: the Political Secretary of the Communist Party, the Chair of the Village People's Committee, and the Chair of the Cooperative.

The Political Secretary, elected by the party members

6 Soils Under Stress

for a two-year term, supervises the implementation of gov­ernmental policies in his village. The Chair of the Village People's Committee, elected by the villagers for a two-year term, is in charge of social welfare programs such as educa­tion, communication, cultural activities/ and social security in the village. He or she also supervises production activities to ensure that production targets are fulfilled. Five associa­tions operate under the aegis of the Village People's Com­mittee. They are the Elders' Association, the Women's Union, the Farmers' Association, the Youth Association, and the Children's Association (or Young Pioneers}. These associa­tions are based on a vertical structure from the national, pro­vincial, and district level to the village level. They have im­portant social and educational functions and also take part in social welfare programs.

The Chair of the Cooperative, elected by Cooperative members for a two-year term, is an executive director of the Cooperative, which is both a collective and centralized pro­duction unit and an organization responsible for its mem­bers' welfare. A village may be composed of two or more Cooperatives, depending on its population and cultivated area. The Cooperative considers applications by new households who wish to join the Cooperative, provides land for housing or homegardens, distributes cultivated land, and organizes the work of production brigades. The Cooperative also dis­tributes rice and necessities to households whose members are sick, disabled, or elderly and unable to work; provides food to schools; supports nurseries and medical clinics; dis­seminates information and gives advice; arranges loans for house construction or for special needs; ensures social secu­rity; and designs development planning.

Operating under the Cooperative are production bri­gades that do all the work for the Cooperative. They are teams of working members from twenty to forty households. Pro­duction brigades are of two types: rice brigades for rice pro­duction; and special brigades for other specific activities such as animal husbandry, handicraft, brick-making, or lime-pro­cessing. After several years of efforts to manage all agricul-

Overview 7

tural production collectively, the government decided to re­turn to a household-based system of management. The change came under Directive No. 10-NG/TW 1988, which relates to the rights of individual households. Under the new policy, the Cooperative no longer regulates daily work or supervises each household's work. The ownership and management of productive materials also changed from a collective to an individual basis. Lands are contracted to individual house­holds on a long-term basis in which tax is collected in re­turn. The Cooperative, however, still controls the land allo­cation, sets guidelines for long-term and short-term planning of production, provides technical advice and service on pro­duction, and organizes other welfare activities.

In the past, the household was the fundamental unit in farming management. With economic reform in Vietnam, farming management has again returned to the household. A common household often consists of two or three genera­tions. Traditionally, both sons and daughters had to live neolocally after their marriage but inheritance of the estate was not equal. Daughters had no inheritance rights, but sons had full rights of inheritance. The eldest son often inherited the house and homegarden and bore the duty of taking care of his parents. The eldest son then became the head of the local patrilineage. Kinship relations play a relatively small part in production because relatives live quite a distance from one another.

LAND USE IN THE RED RIVER DELTA

Because soils in the Red River Delta are renowned for their suitability for paddy rice, almost all cultivated land is used to grow rice. Only a small proportion remains for cash or other crops.

There are two distinct crops: the winter/spring crop from November and December to May and June, and the sum­mer/autumn crop from May and June to October and No­vember. The current improved irrigation system helps local people to control the factors of cultivation. Besides the two

8 Soils Under Stress

traditional crops, local people now grow early spring/sum­mer crops and very early summer crops that favor heat-toler­ant winter crops. Various crop varieties and crops that can grow in water-deficit conditions have been introduced. There are two groups of winter crops: early winter tropical-derived crops and late winter temperate zone-derived crops. Crops in the first group are maize, soybean, sweet potato, onion, and garlic, which can be planted between 20 September and 10 October. The second group includes potato, cabbage, kohl­rabi, and wheat, which can be planted from 20 October to 20 November. Rice varieties with different maturity durations have also been identified, making possible the arrangement of cropping schedules to fit the alternative cropping systems.

NGUYEN XA Nguyen Xa is located in Dong Hung District near the center VILLAGE of Thai Binh Province (see Figure 1.1). Because it is located

in the flat alluvial plain of the Red River Delta, the village is influenced by the climatic environments prevailing in the Red River Delta and by the hydrology of the Thai Binh River system. It is a highly intensive cultivated area and very densely populated. The village is an ancient community with a history,- thus, its patterns of cultural practices and social organization are extremely complex.

POPULATION

The de facto population of Nguyen Xa is 6,512, of which 6,438 were classified as residents as of 31 March 1991. With a total surface area of approximately 430 ha, the village at that time had a population density of 1,497 persons/km2, exceeding the provincial average (1,065 persons/km2) and the average for Dong Hung District (1,122 persons/km2). Calculated on the cultivated-area basis, the village population density is 2,030 persons/km2 of cultivated land. Each hectare must support 20.3 persons. This represents only 490 m 2 (5,272 square feet} of cultivated land area for each inhabitant of the village.

The village population data indicated a major decline

Overview 9

in fertility over the past decade, partly attributable to the family planning campaign. The death rate also decreased but at a slower rate. This mortality decline has partially offset the decline in births so that the population growth rate has remained in excess of 1.5 percent per year. At this rate, the village population will increase by 35 percent in twenty years. Such a population increase places heavy demands on limited land, both for rice fields and sites for houses.

SOCIAL AND POLITICAL ORGANIZATION

The social organization of Nguyen Xa is basically similar to the pattern common to villages in the Red River Delta. The basic units of social structure within Nguyen Xa are the fam­ily and household, neighborhood, and lineage. In addition, various informal and formally recognized associations bring together people with similar interests. The political struc­tures of the village government and the Cooperative are also key in structuring people's lives. Altogether, these social and political structures tie people into a web of social relation­ships and obligations that unite, and sometimes divide, vil­lage society.

The basic social unit is the family. Organization is patrilineal and post-marital residence is patrilocal (i.e., chil­dren receive their family name and social identity from their father, and newly married couples live with that husband's parents). Households are composed of conjugal couples, their children, the wives of their sons, and the children of these couples. Living arrangements are generally "extended," al­though this means co-residence in one house or residence in two or more neighboring houses. Typically, at marriage, sons take up residence near or in the same compound as their parents, whereas daughters most often move close to the homes of their husbands' parents. In some households, par­ents and married offspring with their spouses live together and share resources. In other instances, families function as nuclear units with their parents residing nearby.

The neighborhood is one of the central social structures

io Soils Under Stress

in the village. Despite the importance of "blood" relations, many activities take place among hamlet and lane co-resi­dents. These activities include labor exchange, hamlet secu­rity, and, in the pre-Liberation days, maintenance of a Taoist shrine. Other significant mutual aid is offered at weddings and funerals.

Lineages link people to others within the same village and in the past were the basis for factionalism in the village. In those days, there were three different dinh or communal houses, each formed by different lineages. It is not clear to what extent these traditional cleavages still exist today. The lineages are also highly significant in extending peoples' ties outside the village. Because a large proportion of the village people are traders, lineage ties give people access to resources and information throughout the region and even on a na­tional level.

Nguyen Xa is unusually large among villages of the Red River Delta. It is divided into eight hamlets [thon] with 23 subhamlets(xoTrj). Several changes in the village division had been done in the past, and the present division has been in effect since 1982. Like other villages in the delta, the village is headed by the Political Secretary of the Communist Party; the Village Committee serves as a legislative and executive arm and the Village Cooperative serves as an executive arm. The village government, however, is relatively small in rela­tion to the total population. The Village Committee and the Village Cooperative each employ thirteen cadre. In addition, four health workers and three nursery school attendants are paid by the village.

The Cooperative is a key element in the village's soli­darity. It has also undergone similar reorganizations as the village and has been consolidated into one villagewide Coop­erative since 1968. The Cooperative provides essential infor­mation to villagers and manages the irrigation system on which all farmers depend. The village and Cooperative also have considerable decision-making powers over the villag­ers' production, although they are now inactive compared to before. The Cooperative allocates land, collects taxes on ag-

Overview n

ricultural production, and distributes funds and offers aid to poor families.

There are many associations in the village. Those offi­cially sanctioned, which are under the auspices of the Com­munist Party, are the Veteran's Association, Women's Union, Farmers' Association, Young Pioneers, Handicrafts Associa­tion, Retired Persons' Association, Soldiers' Mothers Asso­ciation, and Communist Youth. There are also traditional, voluntary, and auxiliary associations. Each adult villager ap­pears to be a member of one or two of these associations.

LAND DISTRIBUTION AND TAX

Following the change in government policy to turn to house­hold-based agricultural production, the land, although allo­cated to individual households, still belongs to the govern­ment. The households have use rights to the land, which, in principle, means life-time use and can be inherited by their children. However, district officials say that agricultural land is reallocated every ten years. Marked differences in the size of residential lands among households observed indicated that residential property can actually be bought, sold, and inher­ited in Nguyen Xa.

Four types of land are allocated among the residents of Nguyen Xa: residential land, the 5 Percent Land (also known as "family land"), the First Land Fund, and the Second Land Fund. The last two types are lands for cropping. In the land allocation system, every household has a right to 240 m 2 of residential land. The 5 Percent Land was first allocated in i960 and again in 1985; therefore, only residents born before 1985 possess this type of land. The First Land Fund was allo­cated in 1988 based on household size: one sao (360 m2) per member.regardlcss of sex and age. Only adults who were not farming at that time did not get a share in the First Land Fund, which is about 80 percent of the total available land in the village. The Second Land Fund is granted only to those households who can show a need for more land or to newly weds where women come from another village. It was also

12 Soils Under Stress

allocated to village-determined "privileged" households that either earned the right by previous productive records or had sons who served and died in the army. Because of land con­straints, not all households can be given this extra land, which is subject to taxation at a much higher rate.

Although the land allocation system employed has con­tributed to a high level of equitability, it has caused consid­erable fragmentation of landholdings. Each household has several small plots to operate, which reduces a considerable area from productive use (i.e., small bunds must be con­structed to demarcate each household's field).

The relatively high equitability of land distribution in Nguyen Xa is coupled with a tax system that imposes a high burden on agricultural incomes. Land in the First Land Fund is taxed at 28 percent of paddy yield for spring crop, while land in the Second Land Fund is taxed at 65 percent. These rates apply only to production up to the target yield assigned to the plot by the village. If the farmer obtains a yield higher than the target, there is no tax on the surplus. For this reason farmers prefer to get plots of lower-rated land, which is easier to improve and thus exceed the assigned production target. Farmers must pay the full tax regardless of whether they achieve good production or not. In years when crops fail due to major natural disasters, however, the national government may reduce the tax assessment. Five Percent Land is taxed at 15 kg of paddy per sao (415.5 kg/ha) per crop.

Taxes are also assessed on livestock that are slaugh­tered and sold within the village. The tax is 15,000 dong for a pig and 20,000 dong for a buffalo. Live animals sold to buyers from outside the village are not taxed. Likewise, the village does not collect taxes on animals killed for ceremonial pur­poses, although technically taxes should be collected.

Income from nonagricultural activities are less heavily taxed. In addition, "contributions" [gop) are levied on each household for the agricultural development fund, the village social and economic fund, and the Cooperative development fund.

In 1990, the village collected 198,900 kg of paddy from

Overview 13

taxes, with approximately 13 percent sent to the national government as its share. Taxes collected by the village to­taled 285 million dong (approximately US$32,000), of which Nguyen Xa retained approximately 242 million dong (US$27,000) for local use. This collection represents an an­nual local government operating budget of approximately US$4 P e r inhabitant.

LAND USE AND VILLAGE AGROECOSYSTEM

Nguyen Xa covers an area of 429.5 ha, of which 316.5 ha (73-7 percent) is agricultural land and 113.0 ha (26.3 percent) is land for irrigation canals, roads, housing, and homegardens (Table 1.1). The land is in a flat alluvial plain where almost the entire cropland is essentially paddy land. Previously, the land flooded annually, but since the construction of the irri­gation and dike system, which began in 1962, flooding has been brought under control and is no longer a problem. Cur­rently, almost all the cultivated areas have year-round irriga­tion service.

Although rice is the dominant crop produced in Nguyen Xa and most of the cultivated land is used for paddy fields, the village agroecosystem contains several distinct sub­systems (local ecosystems or land-use units). These include

Table 1.1 Nguyen Xa land use

Category Area (ha) Percentage

Agricultural land 316.5 73.7

Cropland 305.4 71.1 Two rice crops 272.0 63.3 Two rice crops and one subsidiary crop 14.8 3.4

Rice nursery 16.2 3.8

Field crops only 2.4 0.6

Ponds 11.1 2.6

Land for specific uses 113.0 26.3 Irrigation canals3 and roads 70.0 16.3 Housing and homegardens 43.0 10.0

Total 429.5 100.0

Source: Nguyen Xa Village Cooperative Office, a. Main canal - S km ; lateral canals - 28 km.

14 Soils Under Stress

Fishpond River

Figure 1.3 Cross-section of Nguyen Xa landscape (Source: Le Trong Cue and Rambo

1993, 18)

cultivated fields (wet rice fields and vegetable fields), houseplots and homegardens, roadsides and dikes, ponds, and canals and the river (see Figure 1.3).

Paddy fields occupy 303.3 ha and vegetable fields 3.4 ha. The government classifies land into seven categories based on physical factors including elevation, quality of water con­trol, and soil type, which are meant to reflect potential pro­ductivity. More than 90 percent of the fields, which yield two rice crops per year, are serviced by the irrigation system. Soils are loamy, ranging from light to heavy in texture. Heavy loams are considered the poorest soil because of high acidity levels.

Two rice crops are grown each year in most paddy fields—the winter/spring crop [vu chiem x u a n ) , which is transplanted in late December to February and harvested in June,- and the summer/fall crop [vu he t h u ) , which is trans­planted in late June to August and harvested in late Septem­ber to October. During the dry winter season, a third crop of sweet potatoes, Irish potatoes, or soybeans and other veg­etables is planted on higher fields (about 83 ha), and corn is grown on lower-lying land (about 36 ha). Some fields (about 16.2 ha) are first used as nurseries for rice seedlings and are then used to grow rice following the transplanting. The vi l ­lage has only 2.4 ha of higher land that is used throughout the year for growing vegetables.

Overview 15

Cultivation of irrigated rice requires skillful manage­ment and is extremely labor intensive. All operations are done manually. Compost from pig and cattle manure is applied heavily, supplemented by chemical fertilizers. Although azolla ( A z o l l a p i n n a t a ) formerly was widely cultivated dur­ing the spring crop as a source of green manure, its cultiva­tion has considerably declined in recent years. After harvest­ing, straw is cut and carried to the house for use in cooking and roofing, and making manure. All tasks must be performed as rapidly as possible since fitting three crops into each year requires extremely tight scheduling. To save precious time, maize for the winter cash crop is sprouted in nurseries and then transplanted into raised beds that have been hurriedly prepared in the newly harvested paddy fields.

There are currently four main varieties of rice grown in the village for the spring crop. Of these, three (VN10, CR203, and CH3) are high-yielding varieties. VN10 is planted on about 70 to 80 percent of the area; CR203 on 5-10 percent of the area, especially on higher areas and areas used earlier in the season as nurseries,- and CH3, a drought-tolerant variety, on 5 percent of the area. A traditional variety of glutinous rice [ l u a nep) is also grown on about 5 percent of the area. For the fall crop, CR203 is dominant, covering about 80 percent of the area. Glutinous rice covers about 15 percent; CH3 about 3 percent, mainly on higher land; and MTL58 about 2 per­cent of the paddies with the best soils. Each year, new variet­ies released by the provincial rice-breeding station are tested on 5 sao of land owned by the Cooperative. Seed from those varieties that perform well are then given to selected farm­ers to multiply in their own plots, with the village buying back the seed at a price of 1.2 kg of paddy for each kilogram of seed. The varieties being grown in the fields are thus gradu­ally replaced every five to ten years.

The houseplots and gardens are raised more than 1 m above the natural surface to provide protection against floods. The soil is mostly very sandy alluvium excavated from low-lying areas next to the settlement area. Most of the surface of each houseplot is taken up by the house and associated

16 Soils Under Stress

structures such as the kitchen, toilet, and pig pen, and a paved courtyard used for drying crops. Homegardens are not as highly developed in Nguyen Xa as they are in some other areas of Vietnam. Ponds are not located within the houseplots and are thus poorly integrated into the garden system. Buf­falo are sometimes kept in stables at the edge of the village rather than near the houses. Pigs are kept on houseplots but are fed primarily with feed brought from paddy fields and ponds. Their manure is recycled to the paddies rather than to the garden. A few chickens range freely through the gardens. Some households keep ducks and pigeons. Wild animal spe­cies are virtually absent.

Space for homegardens on the houseplots is severely limited. The house and paved courtyard commonly occupy most of the central area of the houseplot, leaving only a nar­row perimeter strip of i to 3 m wide for garden use. Trees are generally short (< 5 m) and are widely dispersed rather than densely planted. There are almost no emergent large trees to form an upper-layer canopy.

The roadsides that connect the village to the district and the tops and sides of the major dikes along the irrigation canals are covered with native grass. The grass, which grows thick but is low in nutritional quality, can be freely grazed by cattle in the village. Grazing pressure is severe, however, and the grass rarely exceeds 3 or 4 cm high.

Publicly owned strips along the main roads are planted with trees that belong to the village. The most common spe­cies are x a cu [ K h a y a seneganensis) and bang [ T e r m i n a l i a cattapa). Eucalyptus, coconut palms, kapok, bamboo, and xoan (Melia azedaiach) are planted beside the smaller roads and paths within the village.

Ponds, which cover 11.1 ha in the village, are of two types: (1) to raise fish and (2) to grow aquatic plants for pig fodder. Fish include various species of carp, tench, and tila-pia. Plants grown in the fodder-producing ponds include wa­ter hyacinth, lotus, pistia, and salvinia for pig fodder and water spinach [rau muong) for human consumption. Although ponds are distributed to individual households to manage,

Overview 17

not all families have access to one. Fear of fish theft is a constraint on raising fish and is one reason most ponds are used for fodder production. People dislike adding pig manure in ponds to feed the fish because the water is also used for bathing and washing clothes.

The village is bounded on its northern and eastern cor­ner by the Tien Hung River, one of the many secondary chan­nels that branch off from the Red River as it nears the sea. Its turbid waters, heavily charged with sediment during the flood season, flow into the village via the Thong Nhat Canal. Elec­trically driven pumps at five stations along this canal lift water into the many small lateral canals that distribute it to the fields |see Figure 1.4). Excess water flows through the village and back into the river where the canal intersects it at the Nguyen Bridge. The irrigation water brings some nu­trients into the system as suspended and dissolved sediments. Nutrients leached from chemical fertilizers and pesticide residues are exported downstream.

Canals and rivers are an open access resource. Anyone can fish in them, and fishing pressure is very heavy. People can also freely build bamboo cages for raising fish. The lower banks of the river and canals are planted to taro [ m u n g or Calocasia sp.), and shallow water areas are devoted to water spinach [rau muong, kangkong, lpomoea aquatica) wherever space is available. Aquatic weeds such as water hyacinth are also collected for use as pig feed and green manure.

The 97 buffalo and 10 cattle in the village are used for plowing. The village is short between 15 and 20 head to meet its minimum draft animal requirement. Despite this short­age, the number of buffalo has declined from 128 head in 1988. Shortage of fodder is the main factor limiting livestock numbers.

The existing landscape of Nguyen Xa is the outcome of numerous trade-offs between land use for food production; infrastructure in the form of irrigation canals, dikes, and road­ways,- housing for the living; gravesites for the dead; and pub­lic facilities. So intense are the competitive pressures that no space remains for natural communities.

18 Soils Under Stress

Figure 1.4 Canal and dike system cf Nguyen Xa (Source: Le Trong Cue and Rambo

1993/ 131)

C H A P T E R 2

Nguyen Van Hoan Harold J. McArthur, Jr. Goro Uehara Vy Ton

Evolution of Agricultural Production and Resource Management

Nguyen Xa Village farmers have been involved in intensive rice cultivation for hundreds of years. Because of various physical factors, including location, elevation, and soil com­position, Nguyen Xa has a history of consistently producing some of the highest yields in the Red River Delta. Over the past fifty years, Nguyen Xa farmers have been able to keep ahead of growing population pressure by achieving nearly a fivefold increase in annual rice yields. Discussions with vil­lage leaders and interviews with farmers in different age groups have enabled us to reconstruct key events associated with significant changes in agricultural production in Nguyen Xa. This section presents the findings chronologically and briefly discusses key events, physical occurrences, techno­logical changes, and social, economic, and political events that have contributed to the extraordinary production his­tory of Nguyen Xa.

CHRONOLOGY Historical development of agricultural production in Nguyen Xa, as was obtained from the interviews, could be divided into four periods: the French period, the land reform period, the Cooperative period, and the contract period. Key events and associated changes in the respective periods are summa­rized in Table 2.1 and are discussed in this chapter.

20 Soils Under Stress

Table i . i Chronology of events and agricultural changes

Period/ date Vietnam Nguyen Xa

1935-40 French colonial rule

9/1940 Arrival of Japanese troops in Indochina

5/1941 Formation of Viet Minh

3/1945 End of French rule; Vietnam under Japanese influence

8/1945 Surender of Japan; Viet Minh seized power

9/1945 Ho Chi Minn's Declaration of Indepen­dence

12/1946 Outbreak of Franco-Vietnamese war 1948 France created "State of Vietnam"

under former emperor Bao Dai 1950 Major defeat of French by Viet Minh

along Vietnam/China border Direct U.S. military aid to French in

Vietnam

5/1954 French defeated at Dien-Bien-Phu Initiation of Land Reform

7/1954 Geneva Agreements Division of Vietnam

1956 Rectification of land reform errors in the north

6/1956

Double cropping of traditional rice varieties without use of fertilizer

Second crop often lost to flooding; yields from 60-70 kg/soo (1.7-1.9 t/ha)

High degree of tenancy,- most land owned by 51 families

Strong village support of Viet Minh resistance fighters

French troops stationed in Dong Hung District

Residents fortified village and repelled three attempts by French forces to move through Nguyen Xa on offen­sive against Viet Minh; 92 villagers killed defending village from French soldiers

1958

987 mau (355.3 ha) of land were redis­tributed to former tenant farmers

Two crops of traditional rice varieties grown with use of manure and compost

Yields ranged from 70 to 80 kg/sao (1.9 to 2.2 t/ha)

Formation of first hamlet-level Cooperative

(continued on next page)

Agricultural Production and Resource Management 21

Table 2.1. (continued)

Period/ date Vietnam Nguyen Xa

1960

1960-67

1963 1965

6/1965

1967

1968

1972

Formation of National Liberation Front of South Vietnam

1976 2/1979

1979

1/1981

1982

1986

Introduction of U.S. ground troops in South Vietnam

Beginning of sustained U.S. bombing of North Vietnam

End of sustained U.S. bombing of the North

4/1975 Collapse of Saigon Government

Unification of Vietnam Chinese invasion of Vietnam Limited introduction of household

contract system in agriculture Directive 100, nationwide implemen­

tation of the household contract system

Further agricultural reforms (Directive 10)

Main canal constructed Yields average 100-130 kgfsao

(2.8-3.6 t/ha) with improved water management

Number of Cooperatives varied from 1 to 16

First electric pumps installed

Local forces shot down a U.S. plane near the Cau Nguyen Bridge

681 men conscripted into military service

265 families lost a son in the war Model irrigation and water manage­

ment system completed with 3 gates and 7 pumping stations

Year-round water control to 90 percent of field areas

Yield increases from 6 to over 10 t/ha with introduction of high-yielding varieties (1966-84)

Village Cooperative began to decentral­ize production with issuance of five-year production contracts to individual households

Production contracts extended to 10 years, with longer-term access to land

Farmers tended to increase labor and inputs

Yields approached.300 kgfsao (8.3 t/ha) using improved VN10 and CR203

Note: Columns 1 and 2 of chronology adapted from Hy V. Luong (1992, xv-xix).

ii Soils Under Stress

T H E F R E N C H P E R I O D (1935-54)

During this period, double cropping of rice was possible in certain field areas in Nguyen Xa, but the second crop was often lost to flooding. Only traditional varieties were grown without the use of fertilizer. The most significant aspect of this period for Nguyen Xa farmers was the high degree of tenancy. A n estimated 70 percent of village farmers owned no land; they either worked for or rented communal land or plots of land from the fifty-one landed families. Besides the residential property and the privately held cropland, com­munal lands were commonly divided and held by the king [ly t r u o n g ) , by the various family lineages [ho], and by those belonging to the pagoda [ c h u a ) .

In Nguyen Xa, traditional rice varieties such as Chiem Bau, Chiem Tep, Chiem Chanh, and Chiem Cut were used for the winter crop (October to June). These were tall Japonica varieties (ranging from 1.45 m to 1.60 m high) that were very susceptible to lodging. Other local Indica varieties (Di Huong, Tarn Bac, and Lua Cau), also with tall stalks, were commonly used in the autumn planting (June to November). Yields dur­ing this period have ranged from 60 to 70 kg per sao (1.7-1.9 t/ha). Farmers also planted several glutinous varieties, in­cluding the Japonica varieties Hoa Vang and Nep Bac.

The French colonial period was not without tension. Thai Binh Province was the site of a French military detach­ment. Remnants of French fortifications are still visible to­day on the grounds of the provincial headquarters. There is also a large Catholic church in Thai Binh that dates from the French occupation.

Closer to Nguyen Xa, a number of French troops were garrisoned in Dong Hung District, not far from the site of the present district headquarters. Unfortunately, Nguyen Xa was situated between the French troops and the Vietnamese re­sistance force (Viet Minh) some distance to the west. On 17 February 1950, the French attempted to move through Nguyen Xa as part of an offensive movement against the Viet

Agricultural Production and Resource Management 23

Minh forces. The residents of Nguyen Xa had fortified the village by constructing an earthen wall, 1 m high and 3 m wide at the base and 2 m wide at the top, completely sur­rounding the residential areas. This barrier contained small holes, called "frog holes," in which the residents could hide for protection. Land mines and spikes were placed in the fields surrounding the village. Armed largely with knives, the v i l ­lagers successfully repelled a force of 300 to 400 French troops. Twenty-seven French soldiers were reportedly killed.

On 19 and 29 August of 1950, the French again marched on Nguyen Xa, and again the village defended itself. Displays in the historical museum ( N h a T r u y e n T h o n g ) indicate that, during these two brief encounters, an estimated 2,000 French troops were forced to retreat after 100 soldiers were killed. In all, 92 Nguyen Xa villagers gave their lives defending their community against the French.

T H E L A N D R E F O R M P E R I O D (1956-57)

In 1954/ following the Viet Minh victory over the French at Dien Bien Phu and the temporary partition of Vietnam, Ho Chi Minh initiated land reform in the northern part of the country. Land reform did not reach Nguyen Xa until 1956. At that time, the land of the fifty-one large landowners in Nguyen Xa was confiscated by the government and redis­tributed to landless families (about 70 percent of the village population of approximately 3,500]. During the land reform, 987 m a u * of land were given to farmers who previously had been landless tenants or renters.

The current Cooperative manager commented that during the Land Reform Period, all wealthy landowners were treated harshly by the central government. The people in Nguyen Xa knew that many landowners in Nguyen Xa had actively supported the struggle against the French by con­tributing sizable quantities of their harvest to support the Viet M i n h guerrillas. These people were referred to as "Land­lords of the Struggle" [Dia c h u k h a n g c h i e n ) . Owing perhaps

24 Soils Under Stress

to this sentiment, only two of the fifty-one landowners in Nguyen Xa were convicted of being "ev i l " and subjected to public denunciation.

The village historical museum (built in 1970 as a gift from a retired army officer) has on display a government land reallocation certificate. The document indicates that on 20 July 1956, a family of three received a total of 5 sao1 of rice land, 1 sao and 10 t h u o c 1 of additional land suitable for the third cropping, and 5 t h u o c of pond area.

A brief period of individual ownership followed the Land Reform. During this time, key informants indicated that two crops of rice could be grown with traditional varieties. Man­agement included the application of green manure and ma­nure compost. Yields reportedly ranged from 70 to 80 kg per sao (r.9-2.2 t/ha}. This slight increase can be attributed to the farmers' willingness to provide more input and to better manage their own fields.

T H E C O O P E R A T I V E P E R I O D (1958-82)

In 1958, the first Cooperative was formed, and all Nguyen Xa farmers were required to turn over their individually owned lands to the collective. Between i960 and 1967, the number of Cooperatives in Nguyen Xa fluctuated from one to as many as sixteen. A certain degree of community soli­darity appears to have carried over from the French resis­tance period. In 1968, the individual hamlet-level Coopera­tives were reunited into one village-wide Cooperative. Dur­ing the Cooperative period, farmers were members of locally organized production teams that managed specific activities and fields following detailed guidelines provided by the Co­operative. In addition to rice production teams, the Coopera­tive organized an irrigation team, a pest and disease control team, an animal husbandry team, and a handicraft team that was charged with making bricks and weaving mats.

During this period, several key changes occurred, which collectively resulted in substantial increases in yields. A new

Agricultural Production and Resource Management 25

variety (Tran Chau Cham) was introduced by the national government, along with fertilizer and management recom­mendations. This technological change, coupled with greatly improved water control following completion of the canal and gates, resulted in increased rice yields of 100 to 130 kg per sao (a.8-3.6 t/ha).

In 1960, a main canal was constructed across Nguyen Xa, providing irrigation water from the Tra Ly River and drain­age into the Tien Hung River. The first electric pumps were installed in 1963. By 1972, a model irrigation and drainage system (with 33 km of canals, three main gates, and seven pumping stations) had been completed. This system now provides year-round irrigation and water control to 90 per­cent of the fields in Nguyen Xa.

Yields continued to increase during the Cooperative period as the result of improved water management and in­troduction of improved varieties. A plaque in the historical museum proudly displays the following records:

Agricultural Production Achievements

Year Yield (kg/ha)

1966 6,473

1970 7,380

1981 9,869 1982 10,104

1984 10,028

Another display in the museum records key objectives of the 1985-86 Village Plan:

Activity

Rice production

Population relocation

Goal

• 11,000 kg/ha with input of manure

from 6.2 pigs ; income to be accom­

plished with an average daily lahor

input of 1.3 persons

• Move 300-500 people to New

Economic Zones

• Reduce population growth to 1.5 percent

26 Soils Under Stress

There was no indication of how close the Cooperative came to meeting these goals in 1986. By 1991, however, the village reported 11 t/ha yields and a population growth rate of exactly 1.5 percent. The accuracy of these figures may be questionable, but what is clear from the plan, and subsequent actions of the Cooperative, is that the people of Nguyen Xa realize that their survival as a village wi l l depend on their ability to balance agricultural production with population growth.

T H E UNITED S T A T E S - V I E T N A M E S E W A R (1965-75)

During the 1960s, U.S. forces bombed areas around Nguyen Xa. Displays in the village museum suggest that an Ameri­can aircraft was shot down in 1967 by local forces while at­tempting to bomb the Cau Nguyen Bridge that crosses the Tien Hung River on the far eastern side of the village. As in the previous war with the French, Nguyen Xa responded with a strong sense of solidarity and support for the national war effort. The museum contains a plaque, commemorating medals and citations awarded to the village for the following contributions to the war effort:

• 2 U.S. aircraft shot down

• 681 men conscripted into military service

• 8,123 tons of rice contributed to the war effort

- 286 tons of pork contributed to the war effort

• Supported 265 families who lost a son in the war

T H E C O N T R A C T P E R I O D (1982-92)

In 1982, following the issuance of Directive 100, the Nguyen Xa Cooperative began to decentralize agricultural production by issuing short-term production contracts to individual households. Each household was assigned a certain parcel(s) of land and given a production quota based on the productive capability of the land. The yield tax was based on the as-

Agricultural Production and Resource Management 27

signed quota, and not on the actual yield. If farmers exceeded the specified quota on the land assigned to them, they were free to dispose of the surplus as they wished. This incentive temporarily increased yields, as farmers were wil l ing to ap­ply large quantities of fertilizer. However, because of the short-term nature of the contract, farmers were not will ing to make long-term improvements to the land.

In 1986, the contract period was increased to five years. In 1992, following Directive 10, it was revised again to allow for a ten- to fifteen-year tenure. Although all land is still owned by the Cooperative, farmers now felt that it was worth the effort to make a long-term investment in improving the quality of the assigned land. Consequently, the amount of manure and other organic matter being incorporated into the fields was greatly increased. The year 1992 appeared to have been an excellent year thus far, and farmers hoped that yields for the second crop would be about 240 kg/sao (6.7 t/ha). One key informant said that the highest yield he ever achieved was 300 kg/sao (8.3 t/ha) in 1986, so he knew that higher yields were possible. Such high yields have been made pos­sible through a combination of intensive management and the use of improved varieties (VN10, CR203, and Dac Thanh) that have been bred to fit the double-cropping requirements of the Red River Delta.

C H A N G E S IN

R I C E V A R I E T Y A N D

P L A N T I N G S E A S O N

An important factor contributing to a continuous increase in rice yield is the availability of new improved high-yield­ing varieties. Table 2.2 summarizes the changes in rice vari­eties in Nguyen Xa during the key phases of agricultural de­velopment. The table clearly shows where and how the sig­nificant increases in yields have been achieved.

New varieties with a short duration have made it pos­sible for growing three crops in a year, and planting seasons have been adjusted accordingly. Before the Cooperative pe­riod, Nguyen Xa farmers were barely able to grow two crops of rice. The winter crop was planted in October and harvested about 1 June. The autumn crop was transplanted in early

18 Soils Under Stress

Table 2.2 Rice varieties and cropping calendar during key phases of agricultural development in Nguyen Xa

Season Variety Phase3 Calendar Characteristics

Before 1960 Winter

Autumn

1964-70 Spring

Autumn

Chiem Tep T P Chiem Chanh Flw Chiem Bau Nur Chiem Cut Har Chiem 314

O l d varieties: Nur Tarn Thorn TP Di Houng Flw Tam Bac Har New varieties: 813, 829

Hoa Van (glutin.) Nep Bac (glutin.)

Dong Xuan 1 Nur 1-5 Feb.

Dong Xuan 2 Tram Chau Lun

813 Moc Tuyen

TP Flw Har Nur T P Flw Har

15-20 Dec. 28 Apr.-2 May 10-20 Oct. 1 June

1-5 June 5-20 July 5-15 Oct. 10-20 Nov.

20-25 Feb. 1-5 May 1-5 June 1-5 June 5-20 July 5-15 Oct. 5-20 Nov.

Cold tolerant. Duration: 210-215 days. Height: 1.45-1.60 m. Yield: 70-80 kg/sao.b

Chiem 314 was selected from Chiem Bau in 1956. High quality. Duration: 155-160 days. Height: 1.60-1.65 m. Yield: 90-100 kg/sao, glutinous rice 80-90 kg/sao.

All new varieties except Tram Chiem 314. First spring rice crop (SR-AR-potato). Dong Xuan 1 and Dong Xuan 2 were intro­duced in 1964, Tram Chau Lun in 1967, and Moc Tuyen in 1966.

Winter

1971-82 Early spring

Chiem 314

VN10

Medium spring IR8

Nur TP Flw Har

Nur

TP Flw Har Nur

10-20 Oct. 15-20 Dec. 1-2 May 1-5 June

20-25 Nov.

25 Jan.-2 Feb. 10-15 May 10-15 June 15 Nov.-5 Dec.

VN10 is cold tolerant, high yielding, acid tolerant, was first used in 1975. It was developed from IR8, which was introduced in 1971.

1R8 was early, high yielding, but susceptible to pests, diseases, and cold.

(continued on next page)

Agricultural Production and Resource Management 29

Table 2.2 ( c o n t i n u e d )

Season Variety Phase3 Calendar Characteristics

XI TP 10-15 Feb. VN10 Flw 5-10 May

Har 5-10 June Late spring XI Nur 1-5 Feb. XI and IR22 were introduced in

1965. TP 20-25 Feb. Flw 10-15 May Har 10-15 June

Early autumn XI Nur 1-6 June Yield less than IR8. Early AR followed by potato and spring rice.

TP 20-25 June Flw 15-20 Aug. Har 20-25 Sept.

Med. autumn IR22 Nur 10-15 June Average yield; susceptible to brown leafhopper.

TP 10-15 July Flw 20-25 Sept. Har 20-25 Oct.

Late autumn 1R27 Nur 5-10 June High yield but not stable. TP 5-10 July Flw 5-10 Oct. Har 5-10 Nov.

1982-present Early spring VN10 Nur 20-25 Nov. Yield: 200-250 kg/sao, cold

tolerant, acid tolerant (pH 4-4.5).

TP 25 Dec.-2 Jan. Flw 10-15 May Har 10-15 June

Late spring CR203 Nur 20-25 Jan. Resistant to brown leafhopper; yield: 180-220 kg/sao; first used in 1983.

TP 15-20 Feb. Flw 15-20 May Har 15-20 June Medium yield: 150-160 kg/sao.

Early autumn CR203 Nur 10-15 June TP 30 June-2 July Flw 30 Aug.-2 Sept. Har 1-3 Oct.

Med. autumn. CR203 Nur 20-25 June High yield: 160-180 kg/sao. TP 10-20 July Flw 10-20 Sept. Har 10-20 Oct.

a. Nur - Nursery; TP - Transplanting; Flw - Flowering; Har - Harvesting. b. 1 sao -360 m 1 .

30 Soils Under Stress

July and harvested in mid-November. There was about one month between harvesting of the winter crop and transplant­ing of the autumn rice. During the early 1960s, when the water control system was completed, the introduction of improved shorter-duration varieties and the increased avail­ability of fertilizers led to significant increases in yield and opened up the possibility of a third (spring) crop.

In 1992, additional high-yielding varieties were also being tested. The varieties No. 256 (from Hanoi Agricultural University), Dac Thanh, and Que Trieu had produced 300 kg/sao (8.3 t/ha) under experimental conditions for spring planting, and 200-220 kg/sao (5.5-6.1 t/ha) for autumn plant­ing. These yields are equal to approximately 500 kg/sao/yx, or 13.85 t/ha/yr.

C O N C L U S I O N Since the 1930s, rice yields in Nguyen Xa had increased about fivefold whereas population had tripled. Such a spectacular yield increase had been attained by improving the water con­trol system and using improved crop varieties, manure, fer­tilizers, and other crop management practices. The changes in the government's land-use policy had also provided an in­centive for increasing production. The key question for the future is whether yields can continue to keep ahead of popu­lation growth and meet the demand for better living stan­dards. It appears that yield increases have begun to level off. In 1984, annual yields passed the 10 t/ha level. The most recent estimates suggest that current yields are within the 11 to 12 t/ha. Yields from the new Dac Thanh variety under controlled conditions are at the estimated level of 13.85 t/ ha. Considering current level of management intensity, it would appear that continued genetic manipulation offers the best chance for significant yield increases over the next five to ten years.

N O T E S 1. One sao equals 360 m2. One thuoc equals 14 m 1. There are 15 thuoc to one sao. One hectare

equals 27.7 sao. A third measure­ment commonly used is the m a u , which is 3,600 m2, or 10 sao.

Soil Characteristics and Changes in Their Chemical Properties

T h e abi l i ty of the land to support and sustain a h igh level of

product ion depends on the qual i ty of i ts soils . Undoubtedly ,

long-term cu l t iva t ion of the soils w o u l d induce changes i n

their properties. Such changes w o u l d indicate the long-term

trend i f current practices are cont inued and w o u l d be the

indicators for assessing sustainabi l i ty of land product iv i ty .

A l t h o u g h nutr ient balance analysis is the p r inc ipa l method

for assessing sustainabi l i ty in this study (see Chapter 6), a

long-term trend i n nutr ient deplet ion or accumula t ion can

on ly be speculated on a theoretical basis. A c t u a l changes i n

so i l properties w o u l d ind ica te whether such a projec t ion

w o u l d l i k e l y be true.

T h i s research was a imed at invest igat ing the qua l i ty of

the soils i n N g u y e n X a Vi l lage and examine the changes i n

soi l properties and other indicators that w o u l d reveal pos­

sible threats to long-term susta inabi l i ty of the land resource.

Fortunately, in 1985 when the lands i n N g u y e n X a were to

be allocated to ind iv idua l households, so i l analyses were done

for a l l the fields for land classif icat ion. These data are ava i l ­

able on the land-class map displayed at Coopera t ive head­

quarters. In 1992, an extensive so i l survey of N g u y e n X a was

done by the Cente r for Agr i cu l tu re of T h a i B i n h Prov ince to

reclassify the lands because the so i l nutr ients had been i m ­

proved by the farmers and the previous classification no longer

reflected the actual product ivi ty . So i l analyses were again

done for a l l the fields i n the vil lage. These data were made

available to us, a l l o w i n g us to analyze the changes i n the so i l

properties measured and to speculate on their causes and

consequences. T h e data were verified by field observations

32 Soils Under Stress

and spot-checking, w h i c h presented a better understanding

of the real condi t ions . So i l samples were taken from selected

spots for chemica l analysis, and farmers and vi l lage leaders

were in terv iewed on land use and so i l management.

In this section, we examine the changes i n so i l proper­

ties in N g u y e n X a i n relat ion to cul tura l management and

other so i l characteristics.

OF NGUYEN XA

SOIL T h e land in N g u y e n X a looks rather flat from a distance. A

CHARACTERISTICS closer view, however, reveals a s l ight ly ro l l i ng topography.

Some areas are s l ight ly elevated, but some spots are s l igh t ly

depressed. Topographically, the areas cou ld be classified in to

three categories—high, middle , and low. For the most part,

the low-to-high areas differed less than i to 2 m i n e levat ion.

T h e midd le topographic class occupies the majori ty of the

area. H i g h spots are scattered along the river banks, and l ow

spots are found near the natural canals and waterways. These

topographic classes, w h i c h are associated w i t h different so i l

types, differ to some extent on so i l characteristics.

A c c o r d i n g to the so i l maps of V i e t n a m and T h a i B i n h ,

N g u y e n X a is located i n the a l l uv i a l soils region of the Red

R ive r system w i t h long-term rice cu l t i va t ion . T h e latest so i l

survey i n N g u y e n X a , conducted i n 1992, recorded the fol­

l o w i n g soi l types:

• O l d a l l u v i a l s o i l i n s i d e t h e d i k e system w i t h c l a y h o ­

r i z o n ( P h g ) . T h i s so i l type occupies the largest area and

is located i n the midd le and relat ively l o w spots. T h e

depth of cul t ivated layer is 10-12 c m . It has a moder­

ate-to-heavy loam texture that can ho ld water w e l l ,

m a k i n g this so i l suitable for cu l t iva t ing two crops of

rice in a year. However , soils i n relat ively l ow spots are

often h igh in acidity, as indicated by the presence of

red color Fe(OH) 3 i n standing water.

• O l d a l l u v i a l s o i l w i t h s p o t t e d o r f e r r a l i t e h o r i z o n ( P h ^ ) .

T h i s so i l type covers a smaller acreage than the first

type and is generally located in the midd le and rela-

Soil Characteristics 33

t ive ly high spots. T h e so i l remains ox id ized i n the w i n ­

ter, m a k i n g the clay hor izon ye l low or spotted (indicat­

ing some oxid ized products of iron). T h i s mot t l ed hori ­

zon, w h i c h is often found at 40-80 c m depth, is suit­

able for the t r ip le -cropping sys tem (r ice-r ice-winter

crop). T h e cul t ivated layer, however, is rather t h i n (8-

12 cm), and a h igh rate of fer t i l izer and frequent irriga­

t ion are required to obtain high crop yields.

- Recently d e p o s i t e d a l l u v i a l s o i l w i t h u n i f o r m h o r i z o n

( P h ) . T h i s so i l type occupies on ly a sma l l area and is

found scattered along the banks of the r iver and m a i n

canals. Recent ly deposited, the soi l is re lat ively fertile

and l ight i n texture (sandy loam). Const ra in ts for crop

product ion on this so i l are lack of water i n the w in t e r

and the long distance from the vil lage.

• A l l u v i a l s o i l w i t h sandy h o r i z o n 3 0 - 4 0 cm b e l o w t h e

s u r f a c e ( P h c ) . A l s o covering on ly a s m a l l area, this soi l

type is generally found near the river bank, often occu­

py ing the midd le topographic pos i t ion . T h e so i l was

formed by an earlier deposi t ion of sand layer brought i n

by flood water, w h i c h was later covered by a l l u v i u m to

about 12-14 c m th ick . Water drains fair ly rapidly in

this so i l because of i ts sandy horizon,- therefore, fre­

quent i r r igat ion is required i n growing win te r crops.

• A l l u v i a l s o i l w i t h a c i d s u l p h a t e h o r i z o n ( P h s ) . T h e so i l

survey of 1992 conducted by the Cente r for Agr i cu l t u r e

of T h a i B i n h located this so i l type in some l o w spots.

A l t h o u g h our field observation and spot-checking d id

not show the acid sulphate hor izon , we not iced so i l

clods w i t h these characteristics (yellow spotted, laterite)

along the water canal. T h e p H of the drainage water

was measured, w h i c h showed a value of 3.2 as compared

to a 7.2 p H value of the i rr igat ion water. So i l samples

taken from these spots were analyzed, w h i c h showed a

clear d i s t inc t ion between the acid sulphate so i l and the

other soils (Table 3.1). T h e acid sulphate so i l has a m u c h

lower p H and a lower content of available phosphorus,

34 Soils Under Stress

Table 3 .1 Results of soi il analysis of samples taken during the field study in 1992

Field Available P a

Field Organic no. Depth (cm) Color pH (KCI) matter (%) mg P2O5/100 g soil mg P/kg

128 S 0-15 h 4.29 3.22 21.5 94 128 D 25^5 Yellow 6.26 0.84 7.7 34 122 S 0-15 — 4.85 3.10 24.1 105 122 D 25-35 Yellow 6.04 1.17 5.6 24 5a S 0-15 — 4.59 3.50 22.7 99 5a D 25^5 Blue 5.90 1.45 7.6 33 5b S 0-15 — 5.35 2.95 24.6 108 5b D 25-35 Yellow 6.30 0.56 8.6 38 9a S 0-15 — 4.56 3.28 26.5 116 9a D 25-35 Blue 5.30 1.67 21.5 94 9b S 0-15 — 4.58 3.61 25.5 111 9b D 25-35. Blue 6.30 0.72 8.2 36 19 S 0-15 — 4.33 2.84 22.5 98 19 D 25^5 Blue 4.78 1.45 11.5 50 ASL 0-15 — 2.64 2.72 5.1 22

Exch. Al 3

Exch K^O (cmolc/kg soil)

CEC Ca++ Mg++ (mg/lOOgsoil) Wet Dry (cmolc/kg soil) {cmoIc/kg soil) (cmolc/kg soil)

128 S 13.7 0.64 6.2 18.9 7.1 7.39 128 D 9.0 0.00 0.0 14.8 5.0 8.64 122S 11.4 0.48 0.2. 20.1 5.8 9.45 122 D 13.7 0.00 0.0 17.2 5.0 10.0 5a S 10.9 0.21 0.2 21.0 7.0 9.54 5a D 10.0 0.00 0.0 16.5 4.3 10.3 5b S 12.3 0.00 0.0 20.5 7.2 10.2 5b D 11.4 0.00 0.0 15.5 4.5 9.19 9a S 11.8 0.68 0.3 21.3 6.7 10.2 9a D 13.2 0.00 0.0 20.0 6.5 10.7 9b S 17.6 0.70 0.2 22.3 7.0 10.9 9b D 11.8 0.00 0.0 16.8 5.3 10.8 19S 13.2 1.42 0.2 17.8 5.5 7.56 19D 11.4 0.06 0.1 18.7 5.3 10.3 ASL 5.0 6.43 6.2 19.7 1.3 1.90

Abbreviations: S - surface soil; D - subsoil; ASL - acid sulphate layer. a. 0.1 N H 2SO«. b. No data.

exchangeable potassium, ca l c ium, and magnes ium con­

tents, but i t has a s u b s t a n t i a l l y h igher a l u m i n u m

content.

T h e so i l texture in N g u y e n X a can be grouped in to two

m a i n categories: l ight loam and moderately heavy l o a m . T h e

Soil Characteristics 35

second category is the predominant type and is suited for

r ice cu l t iva t ion . Soils i n the h igh spots are generally l ighter

i n texture and are suited for tuber and other w in t e r crops.

T h e so i l survey of 1992, as w e l l as our so i l sampl ing ,

indicated a considerable var ia t ion i n the th ickness of the

cult ivated layer, ranging from 8-16 c m , among different fields.

General ly , the relat ively high f ield posi t ions have a th inner

cul t ivated layer than those i n the l ow posit ions. T h e th in ­

nest cul t ivated layer (8 cm] was found i n the fields of Phan

Thans and Tran P h u hamlets . Th i cknes s of cu l t iva ted layer

is an important factor de te rmin ing the size of the reservoir

of nutr ient and water supply to the crop; thus, i t has a direct

effect on fert i l izer and i rr igat ion practices. Farmers ' experi­

ences showed that in the area w i t h a t h i n cul t iva ted layer

(< 10 cm}, a high rate of fert i l izer and frequent i r r iga t ion are

required to obtain high crop yields.

SOIL CHEMICAL Table 3.2 summarizes the chemica l properties of N g u y e n X a

PROPERTIES soi ls from the soi l analysis conducted i n 1992. T h e data show

IN 1992 t ha t currently 95 percent of the cul t ivated fields i n N g u y e n

X a are acid. A b o u t 41 percent of the fields have a p H (KCl )

lower than 4.5, and 54 percent have p H values between 4.5

and 5.5. D u r i n g field observation, we not iced several weed

species that are indicators of acid soils . Farmers k n o w that

their fields are acid by these weeds and also by the red color

of field water. Consequently, l i m e applicat ion has been a com­

m o n practice of most farmers. A l t h o u g h our field observa­

t ion and farmer interviews seemed to indicate that strongly

acid soils are associated w i t h l ow spots, the so i l analysis data

did not show such an association. Strongly ac id soils, as w e l l

as acid and s l igh t ly acid soils, were found in fields at a l l to­

pography (Table 3.2). Furthermore, no relat ionship was found

between the level of so i l acidi ty and depth of p low pan.

In 1992, the majority of the fields were high in organic

matter. Eighty-four percent of the fields contained organic

matter content of more than 2 percent (Table 3.2). T h i s find­

ing is not surprising as manure has been regularly applied at

36 Soils Under Stress

Table 3.2 Soil chemical properties of Nguyen Xa and their relationship with land topography and depth of plow pan (1992}

„ , . . , Topography Depth of plow pan (cm) Soil property No. of 1 and class fields % Low Medium High 9-10 11-13 14-16

pH (KC1) Strongly acid (< 4.5) 65 41.1 9 40 16 14 31 20 Acid (4.5-5.5) 86 54.4 8 51 26 18 36 31 Slightly acid (> 5.5) 7 4.4 1 4 2 3 2 2

Organic matter Low|< 1%) 2 1.4 1 1 1 1 Medium (1-2%) 22 15.0 15 7 6 10 5 High (> 2%) 123 83.7 16 76 36 28 57 44

Available P a

Low (< 10 mg) 138 90.1 16 83 38 31 58 48 Medium (10-15 mg) 7 4.5 1 6 73 High(> 15 mg) 8 5.2 2 6 3 2

Exchangeable K b

Low (< 10 mg) 72 100 4 38 30 18 31 23

a. mg of PjCyiOO g soil |0.1 N H 2 SOJ. b. mgof K 2O/100g9oil.

a high rate. Available phosphorus, however, was generally

low. Ninety percent of the fields contained available phos­

phorus, as measured by the Oniani method (0.1 N H 2 S0 4 ) ,

less than 10 mg P 2 O s / ioo g soil. Exchangeable potassium was

low (< 10 mg ICjO/ioo g soil) in all the fields. No relationship

was found among these three soil properties and land topog­

raphy and depth of plow pan (Table 3.2).

CHANGES IN

SOIL CHEMICAL

PROPERTIES

DURING 1985-92

Table 3.3 shows comparisons of the chemical properties of

Nguyen Xa soils measured in 1992 and the corresponding

values measured in 1985. The data indicated that changes

had occurred in all chemical properties, except for exchange­

able K which could not be compared because the 1985 data

were not available. Each property showed fields with posi­

tive and negative changes. Thus, the overall trend reflects

the balance between changes in these opposite directions.

Relationship of the changes with their original class values

in 1985 and with levels of topography and depth of plow pan

Soil Characteristics 37

Table 3.3 Changes in chemical properties of Nguyen Xa soils during 1985-92

Difference 1992 1985 (1992- 1985)

Soil property No. of No. of No. of and class fields % fields % fields %

pH (KC1) Strongly acid (< 4.5) 65 41.1 30 19.1 35 22.0 Acid (4.5-5.5) 86 54.4 100 63.7 -14 -9.3 Slightly acid (> 5.5) 7 4.4 27 17.2 -20 -12.8

Organic matter Low (< 1%) 2 1.3 28 17.9 -26 -16.6 Medium (1-2%) 22 14.4 56 35.9 -34 -21.5 High (> 2%) 129 84.3 72 46.2 57 38.1

Available P a

Low (< 10 mg) 138 90.1 93 59.2 45 30.4 Medium (10-15 mg) 7 4.5 37 23.6 -30 -19.1 High(> 15 mg) 8 5.2 27 17.2 -19 -12.0

Exchangeable K b

Low (< 10 mg) 72 100 NA NA — —

NA - Not available. a. mgof PjCyiOOg soil 10.1 N HjSOJ. b. mgof KjO/lOOg soil.

are presented i n Tables 3.4-3.6 for p H value, organic mat ter

content, and available P, respectively.

For p H value, comparison of the 1992 and 1985 data

indicated an increase i n the number of fields i n the strongly

acid class and a decl ine i n the number of fields i n the ac id

and s l igh t ly acid classes (Table 3.3). Apparent ly , the trend is

toward an increase i n soi l acidity, a l though l i m e is c o m m o n l y

applied and the high p H of i r r igat ion water should have neu­

tralized the ac id i ty to some extent. T h i s increase i n so i l acid­

i ty might be attributed to the release of acid substances from

submerged decomposi t ion of manure and crop residue, w h i c h

are used at high rates, and from the appl icat ion of chemica l

ferti l izers. In some spots, h igh acidi ty migh t be accounted

for by an acid sulphate hor izon i n the so i l .

E x a m i n a t i o n of the d i s t r i b u t i o n of f ields that had

changed i n p H class (Table 3.4) revealed a clear re la t ionship

between the di rec t ion of change and the or ig inal class value

i n 1985. Fields that were strongly acid i n 1985 showed a trend

toward a decl ine in soi l acidity. However , for those f i e l d s i n

38 Soils Under Stress

Table 3.4 Distribution of fields in which pH class changed during 1985-92

Change in pH class (+ - increase; - - decrease)

Category and class -2 -1 0 1 2

1985 pH(KCl) class Strongly acid (< 4.5) 13 16 1 Acid (4.5-5.5) 48 46 6 Slightly acid (> 5.5) 4 23

Total 4 71 59 22 1 Percent 2.6 45.2 37.6 14.0 0.6

Land topography Low 1 7 7 3 Medium 2 41 38 14 High 1 23 13 5 1

Depth of plow pan 9-10 cm 17 11 7 11-13 cm 2 29 29 8 14-16 cm 2 25 18 7 1

Table 3.5 Distribution of fields in which organic matter class changed during 19S5-92

Change in organic matter class (+ - increase; - - decrease)

Category and class -2 -1 0 1 2

1985 Organic matter Low (< 1%) 4 22 Moderate (1-2%) 1 7 47 High|>2%) 1 10 59

Total I 11 66 51 22 Percent 0.7 7.3 43.7 33.8 14.5

Land topography Low 1 5 11 Medium 6 42 26 16 High 5 19 13 6

Depth of plow pan 9-10 cm 2 12 14 6 11-13 cm 1 6 31 17 12 14-16 cm 3 23 19 4

Soil Characteristics 39

Table 3.6 Distribution of fields in which available phosphorus class changed during 1985-92

Change in available P class (+ - increase; - - decrease)

Category and class -2 -1 0 1 2

1985 available Pa

Low (< 10 mg) 86 2 2 Moderate (10-15 mg) 31 4 2 High {> 15 mg) 20 .1 4

Total 20 32 94 4 2 Percent 13.2 21.1 61.8 2.6 1.3

Land topography Low 1 3 13 Medium 11 23 54 3 High 8 6 26 1 2

Depth of plow pan 9-10 cm 17 11 7 11-13 cm 2 29 29 8 2 14-16 cm 18 7 1

a. mgof PjO s/100gsoil.

the acid and s l ight ly acid classes in 1985, the changes were

toward higher acidity. A possible explanat ion might be a se­

lect ive appl icat ion of a high rate of l i m e on ly i n strongly ac id

fields but not i n fields w i t h less acidity. N o rela t ionship was

observed between changes i n soi l ac id i ty and land topogra­

phy or depth of p low pan.

T h e trend i n increasing levels of organic matter con­

tent i n the soils was quite apparent. There were signif icant

decreases i n the number of fields i n the l o w and m e d i u m

classes and a substantial increase i n the number of fields i n

the high organic matter class (Table 3.3). Cur ren t ly , 84 per­

cent of the fields have h igh organic matter content (> 2 per­

cent). A l t h o u g h a l l the fields i n the l ow class and most of the

fields i n the m e d i u m class in 1985 changed to the higher

levels, most of the fields in the h igh organic matter class

remained unchanged (Table 3.5). T h i s was undoubtedly the

consequence of a h i g h rate of manure a p p l i c a t i o n . T h e

changes i n organic matter content, however, were not asso­

ciated w i t h land topography or depth of p l o w pan.

Changes in available P, on the other hand, showed a

40 Soils Under Stress

dec l in ing trend. From 1985 to 1992, the number of fields i n

the high class decreased from 27 to 8 and those i n the me­

d i u m class decl ined from 37 to 7, whereas fields i n the l o w

class increased from 93 to 138 (Table 3.3). Cur ren t ly , 90 per­

cent of the fields are in the l ow available P class (< 10 m g

P 2 O s / i o o g soil). D i s t r i b u t i o n of changes also showed the

opposite of what was observed for the changes in organic

matter. A l t h o u g h most fields i n the high and m e d i u m classes

changed to the lower classes, most fields in the l o w class

remained the same (Table 3.6). A g a i n , no clear re la t ionship

was found between changes in available P and land topogra­

phy or depth of p low pan, except that fields w i t h a deep p l o w

pan (14-16 cm) showed no decl ine in available P, and some

even showed an increase.

T h e decl ine i n available P was unexpected since the

nutr ient balance analysis showed a substantial posi t ive bal­

ance for P (see Chapter 6). It might be that the appl ica t ion

rates of P fert i l izer i n the early years were not as h igh as the

current rates. T h e decreasing level of so i l p H also suggested

that so i l adsorption capacity might be increasing and that

the surplus P might be fixed i n the nonavai lable form, re­

su l t ing in a decl ine rather than an increase i n so i l test P.

Whatever the reason, the decl ine i n avai lable P suggested

that the use of P for plant growth i n these soils migh t be

inefficient.

A l t h o u g h changes in exchangeable K cou ld not be ex­

amined due to the unavai lab i l i ty of the 1985 data, the nega­

t ive balance of this nutr ient indicated by the nutr ient bal­

ance analysis (Chapter 6) suggested that the changes w o u l d

l i k e l y be on a dec l in ing trend. Cur ren t ly , a l l the fields i n

N g u y e n X a are already l ow in K, and the appl icat ion of K is

not a c o m m o n practice. If the current practice cont inues ,

this nutr ient w o u l d cer ta inly be a l i m i t i n g factor for crop

product ion in N g u y e n X a .

Soil Characteristics 41

C O N C L U S I O N The alluvial soils with light loam to moderately heavy loam texture prevailing in Nguyen Xa are well suited for rice cul­tivation. The lighter texture in the relatively high spots also makes the soils suitable for growing winter crops. With an efficient irrigation system and high rates of manure and fer­tilizers, the land can support an intensive cropping system and high yields.

However, the Nguyen Xa soils are not without prob­lems. The soil analysis of 1992 indicated that currently most of the fields are high in acidity, more so in certain spots where an acid sulphate layer may be buried. Evidence shows that soil pH has been declining since 1985, despite the common application of lime and the neutralizing effect of irrigation water. The increased level of organic matter, presumably due to heavy application of manure and night soil, is a good sign, but might have contributed to the declining level of soil pH. Certainly, management of soil acidity w i l l play an impor­tant role in the long-term sustainability of land productivity in Nguyen Xa.

Despite a substantial annual positive balance of P sug­gested by the nutrient balance analysis, the level of available P in the soils appears to be declining. This finding suggests that the use of this nutrient to support crop growth might be inefficient, and further investigation in this area is needed. Improving the management of P in the soils appears to be another area that deserves attention.

Finally, all the fields in Nguyen Xa are already low in K content. The nutrient balance analysis also showed a nega­tive balance, indicating that a substantial amount of K is drawn from the soils annually. Clearly, this nutrient is of most concern to the sustainability of land productivity of Nguyen Xa.

C H A P T E R 4

I ran Danh Thin Goro Uehara

Contribution of Sediment to Nutrient Flow

Sediment is a source of nutrients that enter the Nguyen Xa Village agroecosystem through flooding and irrigation water. In the old days when the village was subjected to annual flood­ing, sediment was undoubtedly an important source of in­coming nutrients and perhaps was the most important fac­tor for maintaining the productivity of the village's land re­source. However, since the completion of the water control and irrigation system in the Red River Delta and Nguyen Xa, flooding has been largely brought under control, and the source of nutrients from flood sediment has also been lost. Currently, the only source of sediment is irrigation water, which loses much of its sediment load before it reaches the fields. Nevertheless, it is still a source of incoming nutrients to the village agroecosystem. In this section, the current con­tribution of sediment to the nutrient flow in Nguyen Xa was estimated as part of the overall nutrient balance study.

P R O C E D U R E The assessment procedure involved estimating the amount of sediment deposited each year in the irrigated fields and converting it into amount of nutrient elements. The amount of sediment deposited each year was estimated by determin­ing ( i ) the volume of irrigation water-applied to the fields, (2) the sediment concentration of the irrigation water, (3) the volume of excess water draining off the fields, and (4) the sediment concentration in the drainage water.

Information on the management of the village irriga­tion system and irrigation practices at the field level was obtained by interviewing the Cooperative manager, a member

44 Soils Under Stress

of the irrigation team, and selected farmers, and by field ob­servation. In June 1992, samples of irrigation and drainage water were taken from several locations and analyzed for sediment concentration.

I R R I G A T I O N

S Y S T E M A N D

I R R I G A T I O N

P R A C T I C E S

Nguyen Xa is bounded on its northern and eastern corner by the Tien Hung River, one of many secondary channels that branch off the Red River as it nears the sea. The water from Tien Hung River flows to Nguyen Xa via the Thong Nhat Canal that runs through the village (see Figure 1.4). Excess water also flows back into the river via this canal as it re­enters the Tien Hung River at the Cau Nguyen Bridge on the far eastern side of the village. There are two gates and five pumping stations along the Thong Nhat Canal. The gates can be opened or closed to raise and lower the water level in a particular section of the canal. Water from the canal is pumped into small lateral canals that distribute it to the fields. In addition, six pump boats operate, as necessary, from the Tien Hung River and a small tributary that meanders across a field. The irrigation system was designed so that every field can be irrigated throughout the year and excess water can be drained out.

Normally, the spring rice crop is irrigated weekly for twelve consecutive weeks. Three to five centimeters of wa­ter is applied with each irrigation. Rainfall during the spring cropping season (January to June) is approximately 500 mm and the potential evapotranspiration is about 400 mm.

The summer/autumn rice crop is transplanted in late June or early July, and harvested in October. The crop is ir­rigated eight times, with 3-5 cm of water per irrigation for a total of 240-400 mm of water. Since the autumn crop falls entirely within the rainy season, less irrigation water is applied.

About 40 percent of the farmland is planted to a non-rice crop such as potato, sweet potato, corn, or vegetable immediately following the autumn rice harvest. This crop is

Sediment Contribution to Nutrient Flow 45

irrigated with about 10 cm of water between mid-October and the end of December.

ESTIMATES Results of the analysis of water samples taken in June 1992 OF SEDIMENT showed that the average sediment concentration was 0.08 DEPOSITION kg /m 3 in irrigation water and 0.04 kg /m 3 i n drainage water.

These values are expected to vary with time of year, but esti­mates of sediment gains and sediment losses based on them should give sufficient insights into the amount of sediment deposited each year and the impact long-term deposition may have on soil fertility and sustainability of the agroecosystem.

The amount of irrigation water applied each year was estimated to be 1.0 m. This is the sum of twenty applica­tions of 4-5 cm of water to the two rice crops, and another 10 cm applied to the non-rice crop. Since the amount of sedi­ment brought to the fields in irrigation water is the product of the depth of irrigation water (1.0 m) and the sediment con­centration, the estimated amount was 0.08 kg/m 2 ( i .o m x 0.08 kg/m3).

Not all of the sediment that flows into the fields re­mains there, however. Some sediment returns to the main canal in the drainage water. The total depth of water leaving the rice fields each year is the difference between the amount added and amount lost through evapotranspiration. The amount added is the sum of rainfall (-1,800 mm) and irriga­tion water (-1,000 mm), and the amount lost through evapo­transpiration is about 1,000 mm. This leaves about 1,800 mm or 1.8 m of water, which must be removed annually from the fields. With a sediment concentration of 0.04 kg/m 3 , the amount of sediment removed each year would be 0.072 kg/ m 2 (1.8 m x 0.04 kg/m3).

The difference between the incoming sediment (0.08 kg/m 2) and the outgoing sediment (0.072 kg/m2) is 0.008 kg/ m 2/yr, or 80 kg/ha/yr. This represents the amount of sedi­ment deposited in the fields each year. Apparently, the amount of annual sediment deposition is quite small. If we

46 Soils Under Stress

assume a soil bulk density of i.o mg/m 3, a soil layer i .o cm thick wi l l be produced after 120 years of irrigation with wa­ter from the Thong Nhat Canal.

C O N T R I B U T I O N O F According to Le Trong Cue and Tran Due Vien (1993), the S E D I M E N T TO T H E sediment of the Red River is very rich. The pH varies be-N U T R I E N T F L O W tween 7 and 7.4. On the average, available nitrogen is 0.5

mg/100 g solid; phosphorus 1.17 mg/100 g; and potassium 1.06 mg/100 g. The Thai Binh River sediment, however, con­tains a moderate amount of phosphorus and a much lower amount of potassium than that of the Red River. Since the nutrient content of the sediment in the Tien Hung River was not available, the values of the Red River were used.

With the sediment deposition rate of 80 kg/ha/yr, the amount of nutrients added to the fields were estimated to be as follows: nitrogen = 0.04 kg N/ha/yr ; phosphorus = 0.09 kg P/ha/yr; and potassium = 0.08 kg K/ha/yr. Apparently, con­tribution of sediment to the nutrient flow in Nguyen Xa is negligible.

Our investigation, however, revealed another important role of irrigation water in Nguyen Xa. Measurement of the pH of canal water showed a value of 7.0. This was in strong contrast with the 3.0 p H value obtained from fields with high soil acidity. Like most soils developed from recent sulfur-rich marine sediments, the soils, and particularly the sub­soils of Nguyen Xa, are acid. This acid subsoil has been capped by even more recent, less acid sediment from the flood water of the Red River. The relatively greater thickness of the sedi­ment capping the acid subsoil in and near Nguyen Xa prob­ably gives the soils their high productivity But even the top soil is now becoming acid from heavy application of acid-forming nitrogen fertilizers. It is nearly certain that the high pH of the irrigation water has helped to lessen the negative effect of heavy fertilizer application.

C H A P T E R 5

Pham Tien Dung Nghiem Phuong Tuyen Aran Patanothai

Azolla Production

Azolla ( A z o l l a p i n n a t a ) , a water fern that can fix atmospheric nitrogen, was widely cultivated in Nguyen Xa Village during the spring crop as a source of green manure. However, azolla cultivation in the village has declined considerably since land management was transferred to individual households. The decline was striking when we learned during our field re­search in 1991 that azolla was applied to only 20 percent of paddy land in the spring crop of that year.

Since azolla is an important source of nutrient input to the paddy system, in this study we further examined azolla production in Nguyen Xa. The objective was to probe deeper into the changes of azolla production and the reasons behind those changes. A n informal interview was used to obtain information from the Cooperative manager and a few selected farmers who were considered key informants.

Azolla has been cultivated in Nguyen Xa since the French Period. Gourou (1936) reported that Nguyen Xa was one of a few villages in the Red River Delta that were the primary centers for azolla production. Other villages had to come to Nguyen Xa to purchase "seed" plants for their use.

The Cooperative manager stated that in the 1920s, be­fore the Cooperative period, azolla was cultivated in all the paddy land in the village. During the Cooperative period, Nguyen Xa was designated a multiplication center of azolla. The responsibility for multiplication and distribution was assigned to the azolla production brigade, and seed plants and potassium were provided to farmers as incentives. Con­sequently, azolla production increased during this period.

C H A N G E S IN

A Z O L L A

P R O D U C T I O N

48 Soils Under Stress

Production reached its peak in 1975, at which time the area covered by azolla was about 150 percent (two crops were grown in some areas). After 1975, the incentives were no longer provided, and azolla production dropped slightly. Fig­ure 5.1 shows the estimated percentages of paddy area cov­ered by azolla in the different periods. (The figure was drawn by the Cooperative manager to represent his approximation.)

In 1985, when the production system changed to indi­vidual responsibility, azolla production dropped to about the same level as the pre-Cooperative period. Production further declined to about 80 percent of area coverage in 1989. Sev­eral reasons were given for the production decline: the fear that the fast-growing nature of azolla would retard the growth of new short-straw spring rice varieties, the availability of low-cost nitrogen fertilizer, and the conflict in time of field use between the third crop and azolla production. Nguyen Xa is no longer an azolla multiplication site; thus, Nguyen Xa villagers must now purchase seed plants from other v i l ­lages.

In the 1991 spring crop, azolla cultivation drastically dropped to about 20 percent of area coverage. This drop was attributed to the long periods of cold weather during the spring season of 1989 and 1990, which damaged some rice plants during the flowering period. Many farmers believed that azolla caused the damage as it covered the water surface, making

Figure 5.1 Percent o f paddy area with azolla cultivation in Nguyen Xa (area >ioo percent indicates two crops were cultivated in some fields)

Azolla Production 49

the water colder, and stopped cultivating azolla the follow­ing season. There were, however, farmers who did not be­lieve that azolla was the cause of cold damage. These farm­ers continued to cultivate azolla and helped to clarify the misunderstanding of their neighbors, with assistance from the Cooperative officers. Consequently, many farmers re­sumed cultivating azolla, which resulted in an increase of azolla cultivation in spring 1992.

F U T U R E O F Azolla cultivation has been a tradition of Nguyen Xa villag-A Z O L L A ers for several decades. The farmers in Nguyen Xa know how CULTIVATION t 0 cultivate azolla and realize its value as a source of fertil­

izer to their rice crop. It was surprising that a misunderstand­ing could develop and cause a drastic reduction in the prac­tice. We had the opportunity to interview Mr . Phu of Bac Lang Hamlet who was the first azolla cultivator in Nguyen Xa. He was quite knowledgeable about azolla cultivation, including the need to apply potassium and the benefits of its cultivation. He did not believe that azolla was the cause of cold damage to rice plants. Fortunately, villagers like Mr. Phu understood the problem and helped to clarify the misunder­standing. The practice is again gaining in popularity. The increasing trend is expected to continue, presumably up to the level of 1989, which is about 80 percent of the paddy area.

C H A P T E R 6

Aran Patanothai Russell S.Yost

Nutrient Balances in Relation to Land-Use Sustainability

The increase in agricultural production in Nguyen Xa V i l ­lage over the past fifty years is quite remarkable. The in­crease was achieved by water control, intensive cropping, and use of high-yielding varieties, manure, and nutrient inputs. Currently, all the cultivated lands in Nguyen Xa produce two rice crops per year, and 40 percent have an additional winter crop. Rice yield is also very high, averaging about 9-10 t/yr. Only a few places in the world have achieved such yields. Another outstanding feature of Nguyen Xa is an elaborate nutrient recycling system, which recycles just about every­thing possible to the field in one way or another. Although the Nguyen Xa villagers have done well in managing the soils, the question still remains—How long can the village land continue to support such intensive cropping?

In Chapter 3, we discussed soil quality and examined the changes that have occurred over the past seven years (1985-92J in order to assess land quality degradation. Such an analysis is, in essence, one way of assessing land-use sus­tainability. In this section, we wi l l assess land-use sustain­ability in another way (i.e., by nutrient balance analysis). A negative balance should indicate that under the current prac­tices, the system is losing nutrients. If such practices con­tinue, land quality wi l l degrade, consequently lowering the sustainability of land productivity. A positive balance may also affect land-use sustainability if the nutrient is accumu­lated to the level that it becomes toxic or creates an imbal­ance with other nutrients. Although it wi l l not be possible to predict when the loss of sustainability becomes critical, the analysis should provide a warning for which appropriate

52 Soils Under Stress

intervention should be taken if long-term productivity is to be maintained. We had used this approach in analyzing the paddy field subsystem that occupies the majority of the area in Nguyen Xa and used the results in assessing the long-term sustainability of the village land.

P R O C E D U R E The following procedure was adopted for analyzing the nu­trient balance:

• Obtain a good understanding of land use, nutrient man­agement practices, and nutrient flow among the sub­systems within the village and with systems outside the village.

• Define the subsystems that are significantly different in nutrient input and output, which require separate analysis of nutrient balance.

• Identify the input and output flows of the different sub­systems and obtain quantitative estimates of them.

• Convert the amount of input and output flows into amount of nutrient elements and calculate the balances.

• Assess the effects of variation in the input and output flows of individual nutrients on long-term trends in nu­trient status and, therefore, probable impact on sustain­ability of land productivity.

Much of the information for this analysis was obtained during our initial investigation (Patanothai et al. 1992J. Fig­ure 6.1 presents a hypothetical model, which was used in the informal interview. Nutrient flows at the village and paddy field levels are also briefly described in this chapter. In this study, we concentrated on getting accurate quantitative estimates of the input and output variables for nutrient bal­ance analysis and on obtaining additional information relat­ing to nutrient flow and management. The paddy fields sub­system was selected for nutrient balance analysis because it covers the majority of the village area. A formal survey with

Nutrient Balances 53

SEDIMENTS FERTILIZERS

RAIN

EROSION

A N I M A L FODDER

FUELWOOD, C O A L

INPUT V I L L A G E

S Y S T E M OUTPUT

OTHER C O M M E R C I A L PRODUCTS

LIVESTOCK' FRUITS

RICE VEGETABLES

SWEET POTATO CORN

CASSAVA

Figure 6.1 Hypothetical input-output model of Nguyen Xa (Source: Le

Trong Cue and Rambo 1993, 149)

a questionnaire (see Appendix C | was used to obtain quanti­tative data on input and output from individual fields, and on the land and labor resource of the households who man­age the fields. Fifty-two farmers were interviewed, and data on input and output for 1991 were obtained for 162 fields, which were spread throughout the village. A rapid rural ap­praisal method (Khon Kaen University 1987) was used in obtaining qualitative information, if needed. Associated sec­ondary data were also collected both before and during the field study. Estimates of the nutrient content of the various inputs and outputs were obtained from secondary sources. Although variation in input and output flows, particularly manure and night soil, was clearly evident, fixed values for nutrient concentration were used in the analysis. The esti­mated nutrient concentration values used and the references from which they were derived are listed in Appendix Table 6.1. The contribution from sediments was estimated in this study (see Chapter 4). Input of nutrients from rainfall, sedi­ments, and green manure, and output of nutrients through

54 Soils Under Stress

drainage were not included in the initial analysis but were considered in the final assessment.

N U T R I E N T F L O W S Nguyen Xa is essentially a rice production village, and most AT T H E V I L L A G E 0 f the cultivated land is used for paddy fields. However, as L E V E L described in Chapter i , the village agroecosystem contains

several distinct subsystems. These include cultivated fields (wet rice fields and vegetable fields), houseplots and homegardens, roadsides and dikes, ponds, and canals and the river. Two rice crops are grown each year in most paddy fields, and a third crop of sweet potato, Irish potato, soybean, or corn is grown in the dry winter season on about 40 percent of the paddy land. A variety of vegetables and fruit trees are grown in homegardens. In addition, a small area of 2.4 ha is devoted entirely to vegetables. Every household raises swine, primarily for manure production. Some households have buf­falo or cattle for draft power, but the number is declining due to shortage of fodder. These livestock depend on rice straw and grasses from roadsides and dikes for their feed. Ponds are used for multipurposes: for raising fish, growing aquatic plants for pig fodder, bathing, washing clothes, and other house­hold uses. Although agriculture is the main occupation, many Nguyen Xa villagers also engage in subsidiary activities, some of which use products from crops and animals. As previously mentioned, an impressive practice in Nguyen Xa in manag­ing these enterprises is the elaborate recycling of nutrients.

Figure 6.2 summarizes the nutrient flows among sub­systems within the village system and between the village and outside systems. Most crops and crop residues are con­sumed in the village, fed to livestock, used in making ma­nure compost, or burned for fuel. Almost all manure, night soil, and ashes from fires are returned to the fields as fertilizer.

The principal nutrient inflows are atmospheric nitro­gen carried by rain or fixed by nitrogen-fixing plants, sedi­ments carried in irrigation water, and chemical fertilizers. Azolla is a nitrogen-fixing plant once very widely used, then declined at one time, but its use is increasing (see Chapter

Nutrient Balances 55

5). Catastrophic floods have not occurred for a long time in Nguyen Xa. Sediments that enter by irrigation water repre­sent only a small amount of nutrient inflow (see Chapter 4]. The amount of atmospheric nitrogen deposited by rain is unknown but is unlikely to exceed 16 kg/ha/yr.1 Chemical fertilizers are the major source of nutrient inflow to the vi l ­lage system.

The major outflow of nutrients is through rice grain, of which the main outflows are through tax payments to the central government and export of processed food products. Noodles produced for sale take about 360 tons of paddy per year, whereas wine-making requires an additional 328 tons of paddy per year. With an annual production of about 3,000 tons of paddy per year, and an annual consumption by the population of about 1,950 tons of paddy per year, and other uses, only a small amount remains for direct sale.

Another major outflow of nutrients is through pigs sold out of the village, which amounts to about 100 t/yr. Other outflows are considered minor for this analysis.

$ 6 Soils Under Stress

N U T R I E N T F L O W S

A T T H E P A D D Y

F I E L D L E V E L

Paddy land in Nguyen Xa is well managed. Farmers heavily apply manure to their fields and also add more chemical fer­tilizers. Pig manure compost and night soil are the two main types of organic manure that every household applies in the fields. Some farmers who own or share buffalo or cattle also have access to buffalo or cattle manure.

Pig manure compost is made by putting rice straw, and sometimes grasses, rice husks, and tree leaves, into the pig pen as bedding, then collecting the bedding and manure for use in the fields. The manure is accumulated daily and is applied to the spring and winter crops twice a year.

To compost night soil, farmers put ash in the latrine to mix with human excrement. Only ash from rice straw or plant materials is used. Because a much lesser quantity of night soils is produced than pig manure, farmers prefer to use night soils for winter subsidiary crops (particularly pota­toes) and rice nurseries.

Buffalo or cattle manure is collected only from the stables where the animals are kept at night. The manure is put into the pit near the stable, together with straw left over from animal feeding. When about i ton of manure and straw is accumulated, soil is then put on the top to cover the com­post. A few farmers also add 20 kg superphosphate and 40 kg rice husk to 1 ton of manure in the pits. Buffalo and cattle manure is used the same way as pig manure.

Azolla is the principal source of green manure used in the village. Other green manure crops such as Sesbania are not planted because of limited land. Many farmers, however, use green manure by taking weedy grasses, wild azolla, and sometimes sweet potato vines and peanut plants, putting them in piles in the fields, and covering them with soil. This type of green manuring is done only for the fall rice crop, but not for the spring crop, because the weather before planting the spring crop is cool and unfavorable for decomposition of the grasses.

Chemical fertilizers and lime arc also applied to the fields, supplementing animal manure and night soil. The fer-

Nutrient Balances 57

tilizers used are urea for nitrogen, superphosphate (20 per­cent P 2O s) for phosphorus, and potassium chloride for potas­sium. Some compound fertilizers are also used, but in small amounts. Some farmers, whose fields contain high soil acid­ity, apply lime to their fields.

The following rates of manure and fertilizer applica­tions are recommended: for spring rice, 8.3-13.85 tons ma­nure, 166-222 kg urea, 416 kg superphosphate, and 83 kg K C l / h a ;

2 and for fall rice, 8.3-13.85 tons manure, 11-139 kg urea, 277 kg superphosphate (or 277 kg of N P K compound fertilizer), and 83 kg K C l per ha. 3 Farmers, however, apply manure and fertilizers differently, varying from farmer to farmer and from field to field. Generally, farmers apply a higher rate of manure and also put lime in the fields with poorer soils or with soil acidity problems. Some farmers add night soil in spots with poor plant growth, and others may use night soil to replace part of the manure for the fall rice crop (i.e., if they do not grow a subsidiary crop or the three crop areas are small and extra night soil is available).

Farmers normally apply night soil to their potato crop and animal manure to their sweet potato crop. If there is insufficient night soil, however, they wi l l add manure to the potato crop. If there is extra night soil, they may apply it to the sweet potato crop. Generally, nitrogen fertilizer is ap­plied to both potato and sweet potato, but only some farmers apply phosphorus fertilizer to the two crops. Only few farm­ers apply potassium fertilizer to these crops.

A l l the crop residues are removed from the fields. Rice straw is cut at the base close to the soil surface. A l l of these crop residues, however, are recycled into the field one way or another. Rice straw is used for making compost, for fuel, for buffalo and cattle fodder, and a small amount is used for making some house roofs. The ash from rice straw is used for composting night soil. Rice husks are used for compost, and rice bran is fed to the pigs (subsequently being recycled as manure). Fresh potato and sweet potato vines are used for pig fodder, and the dry vines are used for making compost.

58 Soils Under Stress

The majority of the products from these three crops are re­cycled into the fields through animal manure or night soil. Although it may appear that all the plant biomass, except roots, are removed from the fields, they are later recycled in a different form. As previously discussed, only some parts are taken out of the system.

Figure 6.3 shows the nutrient flows between the two rice-crop fields and the household, and other subsystems in the spring and fall cropping seasons. A similar diagram could also be drawn for the three crop fields, but it would be more complicated.

Chemical Rains, sediments, Tax, sale, and fertilizers and fixation other products

Tax, sale, and Rains, sediments. Chemical Village system other products and fixation fertilizers boundary

Figure 6.3 Nutrient flows between double-cropped rice fields, house­

holds, and other subsystems—spring and fall (Source: Le Trong Cue and

Rambo 1993, 157)

Nutrient Balances 59

H O U S E H O L D S

I N T E R V I E W E D

C H A R A C T E R I S T I C S In the formal survey with questionnaire, fifty-two households 0 F T H E were interviewed, and data on manure and fertilizer applica­

tions and on crop yields for 1991 were obtained for 162 fields. Maximum and minimum yields in these fields were also obtained from farmers' recollection.

The households interviewed varied in size from three to nine persons per household, with the number of farm la­borers from one to six. Table 6.1 shows the distribution of family size and number of farm laborers of these households. The number of fields operated by a household also varied, from two to seven, but the majority of the households had two to four fields (Table 6.2).

Every household raises pigs primarily to produce ma­nure for crop production and as a source of food and additional income. In 1991, the number of pigs raised by the households

Table 6.1 Dis t r ibu t ion of family size and farm laborers

Persons in Household

Farm laborers Househo ld

(no.) N o . % (no.) N o . %

3 9 17.3 1 9 17.3 4 11 21.2 2 16 30.8 5 16 30.8 3 14 26.9 6 8 15.4 4 10 19.2 7 3 5.8 5 2 3.8 8 4 7.7 6 1 1.9 9 1 1.9

Total 52 100.0 52 100.0

Note: Percentages may not total exactly because of rounding.

Table 6.2 Dis t r ibu t ion of number of fields per household

Fields per household (no.)

Household

N o . %

2 22 42.3 3 11 21.2 4 14 26.9 5 2 3.8 6 2 3.8 7 1 1.9

Total 52 100.0

6o Soils Under Stress

Table 6.3 Frequency dis t r ibut ion of households w i t h different number of pigs

N u m b e r of pigs/household

Year 0 1 2 3 4 5 6 7 8 12

1987 3 2 11 14 13 3 3 2 1 1988 2 1 11 15 12 4 4 1 1 1

1989 1 1 13 13 15 3 3 1 2 1990 1 11 17 U 3 7 1 1 1991 1 10 14 15 6 4 1 1

interviewed ranged from one to eight. Table 6.3 shows the distribution of pigs per household during 1987-91. The data indicate that the number of pigs per household remained about the same throughout the five-year period. N o relation­ship, however, was found between number of pigs raised and the number of persons or of farm laborers per household (cor­relation coefficient, r = 0.141 and 0.030, respectively). Nei­ther was the relationship between pig number and total area allocated to the household (r = 0.185).

The amount of pig manure produced by the individual households ranged from 2 to more than 10 t/yr, but the ma­jority of the households produced about 4-8 t/yr (Table 6.4). Night soil was also produced by every household for use as fertilizer. In 1991, 60 percent of the households produced 0.5-1.0 ton of night soil per year, 27 percent less than 0.5 t/yr, and 13 percent more than 1.0 t/yr (Table 6.4).

Table 6.4 A m o u n t of pig manure and night soi l produced by ind iv idua l households in 1991

P i g manure Nigh t soi l

A m o u n t produced It/yr)

Household A m o u n t produced

(t/yr)

Househo ld A m o u n t produced

It/yr) N o . % A m o u n t produced

(t/yr) N o . %

2.0-4.0 11 21.1 <0.5 14 26.9 4.1-6.0 23 44.2 0.5-1.0 31 59.6 6.1-8.0 10 19.2 1.1-1.5 2 3.8

8.1-10.0 6 11.5 1.6-2.0 4 7.7 > 10.0 2 3.8 >2.0 1 1.9 Tota l 52 100.0 52 100.0

Nutrient Balances 61

Table 6.5 Amount of buffalo manure produced by individual households in 1991

Amount produced Household

Amount produced Household

(t/yr) No. %

0 44 84.6 1-3 6 11.5 7-8 2 3.8

Of the fifty-two households interviewed, only seven­teen (33 percent) owned or shared buffalo. The rest (68 per­cent) did not and had to depend on hired buffalo for preparing land. In 1991, only eight households had buffalo manure: six households had 1-3 tons and two had 7-8 tons (Table 6.5}.

The amount of pig manure produced appeared to be re­lated to total area operated by the household rather than to number of pigs raised or number of persons in the household (Table 6.6). This finding confirmed a hypothesis from our informal interview that farmers normally set a target of the amount of manure they would produce each year based on the amount needed for fertilizing all their fields. N o matter how much pure manure is collected from the pigs, they would add rice straw, rice husk, grasses, and weeds to reach the targeted amount. This practice has undoubtedly led to a great variation in quality of the manure and, consequently, to its nutrient contents. Similarly, no relationship was found

Table 6.6 Correlation coefficients between pig manure, night soil, and buffalo manure produced and certain characteristics of households

Production

Variable Pig manure Night soil Buffalo manure

Persons in household 0.287 0.196 0.001 Fields of household 0.291 0.001 0.263 Total area operated by household 0.548 0.078 0.117 Pigs raised by household 0.303 — — Amount used for spring rice 0.968 0.259 0.326 Amount used for autumn rice 0.948 0.210 0.880 Amount used for winter crops 0.211 0.827 0.956 Night soil produced 0.264 — -0.128 Buffalo manure produced 0.230 -0.128 —

6 z Soils Under Stress

between the amount of night soil or buffalo manure produced and the number of persons per household or total area oper­ated by the household (Table 6.6). Also, no relationship was observed among the amount of pig manure, night soil, and buffalo manure produced by the individual households.

Examination of the correlation between the amount produced and the amount used for spring rice, autumn rice, and winter crops revealed that pig manure was used mainly for spring and autumn rice, whereas buffalo manure was used mainly for autumn rice and winter crops. Night soil, how­ever, was used primarily for winter crops (Table 6.6). Table 6.7 shows the distribution of household usages of pig ma­nure and night soils in their respective main cropping sea­sons. The informal interview conducted earlier revealed that farmers consider night soil a better fertilizer than pig ma­nure and generally reserve night soil for winter cash crops.

A question was also asked whether the household pro­duced enough manure for their needs. Of the fifty-two house­holds, thirty-seven replied that they had enough, but fifteen said they did not have enough manure and would like to have an additional 1-4 tons per year. When asked how they intend to solve the problem of insufficient manure, most of them said they would buy rice husk, rice straw, or cut more grasses to put into the manure pit, a few would use chemical fertil­izers, one would grow green manure, and two said they would raise more pigs. Apparently, farmers had already been think­ing about how to solve their problem.

Table 6.7 Use of pig manure and night soil

Pig manure Night soil

Percent used for

spring rice

Household Percent used for

autumn rice

Household Percent used for

winter crop

Household Percent used for

spring rice No. %

Percent used for

autumn rice No. %

Percent used for

winter crop No. %

0 1 1.9 0 1 1.9 0 11 21.2 30-39 2 3.8 20-39 9 17.3 10-40 4 7.7 40-49 18 34.6 40-49 20 38.5 41-60 6 11.5 50-59 28 53.8 50 22 42.3 61-80 4 7.7 60-67 3 5.8 81-100 27 51.9 Total 52 100.0 52 100.0 52 100.0

Nutrient Balances 63

LAND USE As described in Chapter 1, 96.5 percent of the agricultural AND FIELD lands in Nguyen Xa are cropland, of which almost all are CHARACTERISTICS p a fjdy land, and only 2.4 ha (or 0.8 percent) are devoted to

vegetable crops only. A l l the paddy land has two crops of rice, and about 40 percent has an additional crop in the dry winter season. Crops grown as the third crop include sweet potato, Irish potato, maize, and soybean, of which sweet po­tato and Irish potato predominated. Of the 162 fields in which data were obtained, seventy (43.2 percent) were planted to two crops of rice, fifty-six (34.6 percent) were planted to two rice crops and a subsidiary crop, and thirty-six (22.2 percent) were used for rice nursery. Among the fifty-six fields with a three-crop pattern, twenty-seven fields had potato; twenty-two, sweet potato; and seven, maize as the third crop.

Table 6.8 shows the characteristics of fields grown to different cropping patterns. These fields are rather small, particularly the rice nursery. Field size ranges from 144 to 2,280 m 2 for production fields, and only 48 to 360 m 2 for rice nursery fields. In Nguyen Xa, the land is classified into seven classes based on several soil characteristics that supposedly reflect soil productivity. Distribution of fields in the differ­ent land classes does not show a particular association be­tween cropping pattern and land class. However, the two-rice cropping pattern appears to be grown more in the me­dium and low-lying fields, whereas the rice nursery and the three-crop patterns are grown mainly in the higher fields. We had also asked farmers to classify their fields into good, moderately good, and poor soil. Of the 162 fields, sixty-seven (41 percent) were classified as having good soil; fifty-two (32.1 percent), moderately good soil; and forty-three (26.5 percent), poor soil. Although the two-rice cropping pattern is spread in all soil productivity classes (slightly more on poor soil), the rice nursery and the three-crop patterns, particularly the pattern with potato as the third crop, tend to concentrate more on good or moderately good soils.

Table 6.9 shows the distribution of fields with good, moderately good, and poor soils in the different land topogra­phy and land classes. While there is no clear relationship

64 Soils Under Stress

Table 6.8 Characteristics of the fields grown to different cropping patterns

Cropping pattern3

Category SR/AR SR/AR/P SR/AR/SP SR/AR/C RN

No. of fields 70 27 22 7 36 Field size

Average (m2) 818.6 455.9 567.8 882.9 196.7 Range (m2) 144-2,280 144-1,224 216-1,440 384-1,200 48^60

Hamlet (no. of fields) Bac Lang (29) 14 2 4 0 9 De Quang (11) 4 2 1 3 1 Le Tien (46) 18 10 3 1 12 Phan Thanh (20) 9 3 4 1 3 Dong Khe (35) 16 6 6 0 7 Da Giang (12) 6 2 2 0 2 Tran Phu (12) 4 2 2 2 2

Land class (no. of fields) 1 13 10 8 1 15 2 18 8 4 2 9 3 18 7 2 2 10 4 19 2 2 2 2 5 2 3 6 2 7 1

Land topographyb (no. of fields) Low 31 2 2 1 8 Medium 30 5 8 2 13 High 9 20 12 4 15

Soil productivity*1 (no. of fields) Good 18 14 10 2 23 Moderately good 24 11 5 1 11 Poor 28 2 7 4 2

a. SR - spring rice, AR - autumn rice, P - potato, SP - sweet potato, C - corn, RN - rice seedling nursery. b. Classified by farmers.

between land topography and land productivity for the low-lying and medium elevated fields, soil in fields on high el­evation appears to be more productive, as indicated by the higher frequency of fields with good and moderately good soils. Productivity levels of soils in the different land classes are as expected (i.e., the lower the class number, the higher the frequency of better productivity fields). This relationship,

Nutrient Balances 65

Table 6.9 Distribution of good, moderately good, and poor fields in the different land topography and land classes

Soil productivity"

Category Good Moderate Poor Total

No. of fields 67 (41.9}b 52 (32.1) 43 (26.5) 162(100.0) Land topography3

Low 17 (38.6) 11 (25.0) 16 (36.4) 44(100.0} Medium 19 (32.7) 21 (36.2} 18 (31.0) 58(100.0} High 31 (51.7) 20 (33.3) 9 (15.0) 60(100.0)

Land class 1 29 190.6) 3 (9.4) 0 (0.0) 32(100.0) 2 8 (25.0) 15 (46.8) 9 (28.1) 32(100.0) 3 6 (20.7) 12 (41.4) 11 (37.9) 29(100.0) 4 1 (4.0) 11 (44.0) 13 (52.0) 25(100.0} 5 0 (0.0) 0 (0.0) 5 (100.0) 5(100.0) 6 0 (0.0) 0 (0.0) 2 (100.0) 2(100.0) 7 0 (0.0) 0 (0.0) 1 (100.0) I (100.0)

a. Classified by farmers. b. Percent of total in each class.

however, only indicates that farmers are well aware of the

productivity levels of their fields, as both land class and farm­

ers' productivity classification are based on soil productivity.

Table 6.10 shows the distribution of fields in different

combinations of land topography and land classes. N o clear

relationship between these two parameters was observed,

however.

Table 6.10 Distribution of fields with different land topography in different land classes

Land topography

Land class High Medium Low Total

1 7 (21.9)a 8 (25.0} 17 (53.1) 32(100.0) 2 7 (21,9) 17 (53.1) 8 (25,0) 32(100.0) 3 9 (31.0) 9 (31.0) 11 (38.0) 29 (100.0) 4 10 (40.0) 10 (40.0) 5 (20.0) 25(100.0) 5 3 (60.0) 0 (0.0) 2 (40.0) 5 (100.0) 6 0 (0.0) 1 (50.0) 1 (50.0) 2(100.0) 7 0 (0.0) 0 (0.0) 1 (100.0) 1 (100.0)

Total 67 (41.9) 52 (32.1) 43 (26.5) 162(100.0)

a. Percent of total in each class.

66 Soils Under Stress

FERTILIZER INPUT Table 6.11 presents means of fertilizer input and crop yields

AND CROP YIELDS m for rice and winter crops in different cropping pat­

terns. Rates of fertilizer input, however, vary greatly from

farm to farm and from field to field. Table 6.12 shows the

distribution of fields for spring rice, autumn rice, and winter

crops that received fertilizer input at different rates. The data

Table 6.11 Means of input and crop yield for different cropping patterns (1991)

Cropping pattern"

Category SR/AR SR/AR/C SR/AR/P SR/AR/SP

No. of fields 70 7 27 22 Spring rice

Manure (t/ha) 12.94 14.09 13.27 11.87 Night soil (t/ha) 0.46 0.40 0.12 0.57 Urea (kg/ha) 163.10 162.70 139.92 164.14 Superphosphate (kg/ha) 300.79 242.06 295.27 289.14 Potassium chloride (kg/ha) 18.65 7.94 12.35 16.41 Compound fertilizer (kg/ha) 49.21 0.00 63.27 28.41 Lime (kg/ha) 125.00 138.89 102.88 130.05 Azolla (t/ha) 8.31 5.56 8.85 6.82

Grain yield (t/ha) 3.07 3.17 3.43 2.90 Straw yield (t/ha) 10.43 10.60 11.12 10.34

Autumn rice Manure (t/ha) 12.57 14.09 12.35 11.74 Night soil (t/ha) 0.23 0.00 0.21 0.62 Urea (kg/ha) 147.62 144.84 134.26 147.73 Superphosphate (kg/ha) 253.17 230.16 290.12 276.52 Potassium chloride (kg/ha) 18.25 7.94 9.26 10.10 Compound fertilizer (kg/ha) 34.13 0.00 68.42 0.00 Lime (kg/ha) 132.94 99.21 92.59 31.57 Azolla (t/ha) 0.20 0.00 0.00 0.00

Grain yield (t/ha) 5.27 5.44 5.21 5.30 Straw yield (t/ha) 11.71- 12.08 11.58 11.77

Winter crop Manure (t/ha) 1.59 9.31 5.53 Night soil (t/ha) 9.92 5.92 5.18 Urea (kg/ha) 230.16 228.40 97.85 Superphosphate (kg/ha) 337.30 389.92 227.27 Potassium chloride (kg/ha) 26.75 6.31 36.71 Compound fertilizer (kg/ha) 0.00 10.29 12.63 Lime (kg/ha) 0.00 0.00 0.00 Azolla (t/ha) 0.00 0.00 0.00

Grain or tuber yield (t/ha) 2.02 15.28 10.85 Stalk or vine yield (t/ha) 5.78 21.83 15.49

a. SR - spring rice, AR - autumn rice, C •• corn, P - Irish potato, SP - sweet potato.

Nutrient Balances 67

Table 6.12 Distribution of fields at different rates of fertilizer application for rice and winter crops

Percent of fields

Application Spring Autumn Winter Fertilizer rate rice rice crop

Manure (t/ha) 0 0.0 0.8 41.1 1-5 0.0 0.0 5.4

6-10 21.4 25.4 21.4 11-15 52.4 47.6 14.3 16-20 23.0 23.8 10.7 >20 3.2 2.4 7.1

Night soil (t/ha) 0 85.6 91.3 21.4 1-4 9.6 5.6 16.1 5-7 3.2 3.2 30.4 8-11 0.8 0.0 17.9 > U 0.0 0.0 14.3

Urea (kg/ha) 0-50 0.8 0.8 3.6 51-100 3.2 5.6 28.6 101-150 33.3 50.8 17.9 151-200 54.8 40.5 8.9 >200 7.9 2.4 41.1

Superphosphate (kg/ha) 0 8.7 11.1 10.7 1-200 5.6 11.9 17.9

201-400 59.5 60.3 39.3 401-600 25.4 15.1 23.2

> 600 0.8 1.6 8.9 Potassium chloride (kg/ha) 0 73.8 76.2 80.4

28-56 18.3 17.5 1.8 83-97 7.9 6.4 8.9

111-139 0.0 0.0 8.9 Compound fertilizer (kg/ha) 0 81.0 84.9 96.4

1-200 5.5 5.5 0.0 201^00 10.3 2.5 3.6

>300 3.2 0.0 0.0 Lime (kg/ha) 0 70.6 75.4 100.0

1-200 0.0 0.8 0.0 201^00 11.9 8.7 0.0 401-600 16.8 14.3 0.0

> 600 0.8 0.8 0.0 Azolla (t/ha) 0 41.3 99.2 100.0

1-12 6.3 0.0 0.0 13-17 51.6 0.8 0.0 > 17 0.8 0.0 0.0

68 Soils Under Stress

clearly indicate that a high rate of manure was applied to both the spring and the autumn rice crops. The majority of the fields received manure at a rate of 10-20 t/ha, and some even received a higher rate. There was no clear difference between the rates of manure applied to spring and autumn rice nor to the corresponding rice crop in the different cropping patterns. Little night soil was applied to the rice crop. On the contrary, night soil was used mainly for winter crops. The rate varied from o to more than 11 t/ha. Corn receives a higher rate of night soil and a lower rate of manure than potato and sweet potato, but this could be because of sampling variations as the number of fields grown to corn is only seven fields.

Similarly, rates of nitrogen, phosphorus, potassium, and compound fertilizers and lime applied to spring and autumn rice were about the same. However, azolla was applied to spring rice only. The main differences in fertilizer input ap­pear to be the rates of fertilizers applied to the different win­ter crops and between the rates applied to rice and winter crops. Corn and potato received a higher rate of nitrogen and phosphorus fertilizers than sweet potato (Table 6 . 1 1 ) . The average rates of potassium and compound fertilizers are rather small for both rice and winter crops, and the majority of the fields did not receive any of these two fertilizers (Table 6.12).

The percentage of rice fields with no lime application was also high (71 percent for spring rice and 75 percent for au­tumn rice). This might account for the variation among rates of lime applied to rice crops in the different cropping pat­terns. No lime, however, was applied to winter crops.

Grain yields of spring rice were considerably lower than those of autumn rice (3 t/ha versus 5 t/ha). This was attrib­uted to the unusually cold weather that damaged some of the spring rice crop at the flowering stage in 1991. Straw yields, however, were not much different, as the estimates were based on the assumption that the rice plants would grow normally and that cold weather only affected the grains. The same yields were obtained for the corresponding rice crop grown in different cropping patterns. Average tuber yield of potato was 15.2S t/ha, compared to 10.85 t/ha for sweet po-

Nutrient Balances 69

tato. Corn gave an average grain yield of 2 t/ha, much lower

than those of other crops.

During the informal interview, farmers stated that they

normally applied higher rates of manure and fertilizer to the

fields that they considered were of poor quality. Table 6.13

shows the average rates of fertilizer input and crop yields for

Table 6.13 Means of input and crop yield for different soil fertility classes

Soil productivity class

Category Crop3 Good Moderate Poor

No. of fields Rice 44 41 41 WC 26 17 13

Fertilizer Manure (t/ha) SR 13.19 12.23 13.21

AR 12.85 11.79 12.73 WC 4.01 2.88 2.19

Night soil (t/ha) SR 0.33 0.37 0.51 AR 0.20 0.22 0.43 WC 3.89 2.54 1.66

Urea (kg/ha) SR 147.10 159.89 168.70 AR 136.68 140.24 157.52 WC 117.42 59.96 -56.23

Superphosphate (kg/ha) SR 284.09 311.65 287.94 AR 282.83 251.36 256.10 WC 200.76 126.02 94.85

Potassium chloride (kg/ha) SR 20.83 10.84 16.94 AR 17.68 12.20 12.87 WC 9.47 10.16 6.78

Compound fertilizer (kg/ha) SR 57.45 29.47 49.80 AR 39.14 45.05 16.26 WC 0.00 6.78 6.78

Lime (kg/ha) SR 59.97 115.18 195.12 AR 72.60 118.56 125.34 WC 0.00 0.00 0.00

Azolla (t/ha) SR 9.09 7.25 7.62 AR 0.32 0.00 0.00 WC 0.00 0.00 0.00

Crop yield Grain (t/ha) SR 3.20 2.98 3.19

AR 5.34 5.25 5.22 WC 7.94 5.01 2.70

Straw or vine (t/ha) SR 10.89 10.57 10.23 AR 11.86 11.67 11.59 WC 11.49 7.25 4.09

a. SR - spring rice, AR - autumn rice, WC - winter crop.

70 Soils Under Stress

the two rice crops and winter crops grown on fields classified by farmers as good, moderately good, and poor. These aver­ages were compiled from data obtained from the formal sur­vey. In general, there was no difference in the rates of ma­nure and fertilizer applied to fields in different soil produc­tivity classes, except for lime (the application rate increased as soil productivity decreased) and for phosphorus and potas­sium fertilizers for winter crops (the application rates appeared to be higher in good soil).

Rice yields in different soil productivity classes were about the same in both the spring and autumn crops. Yields of winter crops, however, were higher in the fields with mod­erately good and good soils.

Similar results were obtained when the rates of fertil­izer input for the different land classes were examined (Table 6.14). Classes 1 and 2 fields could be considered as having good soil; Classes 3 and 4, moderately good soil; and Classes 5-7, poor soil. The only clear relationship observed is the increased rate of lime in poor soil. This is presumably be­cause soil acidity is one of the criteria for land classification and one that farmers use to classify soil productivity. The rates of other input are about the same for different land classes. Some differences among land classes, however, were observed on phosphorus and potassium fertilizer rates for winter crops. This could be accounted for by differences in the kind of winter crop grown in different land classes.

Rice yields in the different land classes were also not much different. The average yield of spring rice of land Classes 5-7 (poor soil) was even slightly higher than that of land Class 1 (good soil). This indicates that farmers had already improved the land to the level that there is not much difference among land classes regarding productivity of the rice crop grown under submerged conditions. Yields of winter crops, how­ever, stil l show a decreasing trend from Class 1 to higher class numbers, or from good soil to poorer soils. Apparently, the inherent inferior characteristics of poor soils have not been overcome under the dry land management of winter crop cultivation.

Nutrient Balances 71

Table 6.14 Means of input and crop yield for different land classes

Land class

Category Crop 3 1 2 3 4 5-7

No. of fields SR, AR 32 32 29 25 8 WC 19 14 11 6 6

Fertilizer Manure (t/ha) SR 12.45 14.54 12.79 11.73 12.33

AR 12.04 13.76 12.96 10.95 12.15 WC 5.34 8.13 8.46 3.24 9.36

Night soil (t/ha) SR 0.20 0.39 0.43 0.42 0.89 AR 0.00 0.09 0.31 0.41 1.70 WC 6.15 7.64 4.80 6.48 3.82

Urea (kg/ha) SR 148.15 153.65 151.34 180.00 166.67 AR 141.67 141.93 142.72 152.78 149.31 WC 209.06 167.66 189.39 143.52 108.80

Superphosphate (kg/ha) SR 250.00 299.48 296.93 321.11 326.39 AR 271.30 270.83 257.66 242.22 302.08 WC 267.54 355.16 434.34 254.63 248.84

Potassium chloride (kg/ha) SR 12.96 7.81 23.95 15.56 31.25 AR 10.19 3.47 25.86 12.22 31.25 W C 11.70 17.86 40.40 32.41 0.00

Compound fertilizer (kg/ha) SR 36.11 20.83 61.78 45.56 43.40 AR 24.07 18.23 58.91 28.89 0.00 WC 0.00 0.00 25.25 0.00 57.87

Lime (kg/ha) SR 41.67 99.83 129.31 200.00 270.83 AR 69.44 65.10 119.73 166.67 173.61 W C 0.00 0.00 0.00 0.00 0.00

Azolla (t/ha) SR 8.52 7.12 9.91 4.78 10.76 AR 0.00 0.00 0.48 0.00 0.00 WC 0.00 0.00 0.00 0.00 0.00

Crop yield Grain (t/ha) SR 2.90 3.68 3.38 2.36 3.23

AR 5.31 5.31 5.15 5.44 4.86 WC 13.80 12.22 11.45 8.98 8.03

Straw or vine (t/ha) SR 10.79 10.63 10.69 10.29 9.91 AR 11.80 11.81 11.44 12.10 10.80 WC 19.88 17.77 17.01 13.76 11.47

a. SR - spring rice, AR - autumn rice, WC - winter crop.

In the formal survey, we had also asked farmers for the

highest yield and lowest yield they ever had for each crop in

each field for the past ten years. Table 6.15 shows means and

ranges of maximum and minimum yields of each crop, com­

pared to the actual yields in 1991. Distribution of fields at

different yield levels for the individual crops are also given

7 i Soils Under Stress

Table 6.15 Means for minimum, yields of different crops

actual (in 1991), and maximum

Crop

Yield (t/ha)

Crop Minimum Actual 1991 Maximum

Spring rice Grain

Mean 2.97 3.12 5.83 Range 1.39-5.56 0.78-6.67 4.17-7.50

Straw Mean 6.61 10.57 12.96 Range 3.09-12.35 7.41-14.81 9.26-16.61

Autumn rice Grain

Mean 3.85 5.27 5.49 Range 1.67-5.56 3.33-7.22 3.33-7.78

Straw Mean 8.55 11.71 12.20 Range 3.70-12.35 7.41-14.07 7.41-17.28

Maize Grain

Mean 1.23 2.02 2.18 Range 0.83-1.94 0.83-2.78 1.11-2.78

Stalk - Mean 3.51 5.78 6.24

Range 2.38-5.56 2.38-7.94 3.17-7.94 Irish potato

Tuber Mean 11.19 15.28 17.79 Range 5.56-18.06 9.72-23.61 11.67-27.78

Vine Mean 15.98 21.83 25.42 Range 7.94-25.79 13.89^33.73 16.67^9.68

Sweet potato Tuber

Mean 6.39 10.85 12.07 Range 2.22-11.11 5.56-16.67 8.83-16.60

Vine Mean 9.13 15.49 17.24 Range 3.17-15.87 7.94-23.81 11.90-23.81

in Table 6.16. The yield of spring rice in 1991 was near the

minimum (because of the damages from cold weather), but

yields of autumn rice and the three winter crops were near

the maximum. Ranges of yields for individual categories,

however, were still considerably wide. For example, maxi-

Nutrient Balances 73

Table 6.16 Distribution of fields at different yield levels for individual crops

Minimum Actual Maximum Minimum Actual Maximum Yield level yield yield yield yield yield yield

Spring rice (% of fields) Autumn rice (% of fields)

Grain (t/ha) <2 27.0 28.6 0.0 2.4 0.0 0.0 2-4 58.7 48.4 0.0 54.0 2.4 0.8 4-6 14.3 20.6 64.2 43.6 88.1 79.4 >6 0.0 2.4 35.7 0.0 9.5 19.8

Straw (t/ha) <9 73.0 11.9 0.0 56.4 2.4 0.8

9-11 21.4 59.5 5.6 33.3 15.9 11.1 11-13 5.6 25.4 58.7 10.3 71.4 67.5 > 13 0.0 3.2 35.7 0.0 10.3 20.6

Irish potato (% of fields) Sweet potato (% of fields)

Tuber (t/ha) < 10 37.0 11.1 0.0 95.5 45.5 27.3

10-15 51.9 40.7 22.2 4.5 50.0 63.6 15-20 11.1 40.7 66.7 0.0 4.5 9.1 >20 0.0 7.4 11.1 0.0 0.0 0.0

Vine (t/ha) < 15 37.0 11.1 0.0 95.5 45.5 27.3

15-20 48.1 33.3 22.2 4.5 45.5 59.0 20-25 14.8 33.3 25.9 0.0 9.0 13.7 2 5 ^ 0 0.0 14.8 40.7 0.0 0.0 0.0 >30 0.0 7.4 11.1 0.0 0.0 0.0

Maize (% of fields)

Grain (t/ha) < 1 14.3 14.3 0.0 1-2 85.7 28.6 28.6 2-3 0.0 57.1 71.4

Stalk (t/ha) <3 14.3 14.3 0.0 3-5 71.4 0.0 14.3 5-7 14.3 71.4 57.1 > 7 0.0 14.3 28.6

mum grain yields for spring rice ranged from 4.17 to 7.50 t/

ha, and for autumn rice, from 3.33 to 7.78 t/ha. These yield

gaps suggest that there might be some possibilities for fur­

ther improvement to raise the yield level of lower yielding

fields, and thus closing these gaps. However, more detailed

74 Soils Under Stress

investigations are needed to examine these possibilities, both technically and economically.

BALANCES OF The foregoing discussion points out that every field is differ-NUTRIENTS ent in terms of nutrient input and output. In practice, it will

not be possible or desirable to assess long-term sustainabil­ity of land productivity for each field. Rather, assessment should be done for each group of fields, which is homoge­neous enough but significantly different from another group, in terms of nutrient input and output to constitute a sub­system. Although there will still be considerable variations within each group, such variations will not warrant further group subdivision and will have to be considered internal variations.

In our initial study (Patanothai et al. 1992}, for the pur­pose of nutrient balance analysis, we divided the paddy land into groups based on cropping patterns and soil productivity (good and poor soils), since, at that time, these two charac­teristics appeared to be the major factors determining the differences between amount of nutrient inflow and outflow at the field level. As discussed, different soil productivity classes do not differ from one another in rates of fertilizer input (except lime) or in terms of crop yields. Therefore, in the following nutrient balance analysis, only the cropping pattern was used in differentiating the paddy fields into groups or subsystems.

Figures 6.4 and 6.5 show the models of nutrient flows for the double-cropped rice fields and the triple-cropped fields (two rice and a winter crop). For each field group (subsystem), the amount of input and output variables was converted to nutrient elements (N, P, K, Ca, Mg, and S), and the balances were calculated. Since fertilizer input and yield data are avail­able for each field, calculations of input, output, and balance of nutrient elements were done for each field, and the results were used in computing group averages.

Nutrient Balances 75

Night soil Manure N fertilizer P fertilizer K fertilizer

Sediments

Rainfall

Compound fertilizer

Rice • Rice

7 Rice

Azolla

Straw Grain Drainage Leaching

Figure 6.4 Nutrient flows for double-cropped rice fields

Night soil Manure N fertilizer P fertilizer K fertilizer

Sediments

Rainfall

Compound fertilizer

Rice - Rice • Sweet Potato

Azolla

Rice Sweet potato

Straw Grain Tuber Vine Drainage Leaching

Figure 6.5 Nutrient flows for triple-cropped fields

Table 6.17 presents the average input, output, and bal­ance of each nutrient element (N, P, K, Ca, Mg, and S) for the four main cropping patterns in Nguyen Xa. All nutrient ele­ments, except K, show positive balances for all the cropping patterns. The amounts, however, vary among nutrient ele­ments and cropping patterns. Total balances for different crop­ping patterns of the individual nutrient elements were 55-146 kg/ha/yr for N, 77-136 kg/ha/yr for P, 270-398 kg/ha/yr

76 Soils Under Stress

Table 6.17 Means for input, output, and balance of nutrient elements for different cropping patterns

Cropping pattern3

Crop Flow SR/AR SR/AR/C SR/AR/P SR/AR/SP

N (kg/ha/yr] SR Input 142.66 133.77 134.35 134.42 SR Output 84.12 86.11 91.52 81.60 SR B a l a n c e 5 8 . 5 4 4 7 . 6 6 42.83 52.82 A R Input 113.20 111.05 109.98 108.11 A R Output 116.43 120.15 115.16 117.06 AR B a l a n c e -3.23 - 9 . 1 0 - 5 . 1 8 -8.95 W C Input 163.30 166.89 92.03 W C Output 55.99 114.40 59.50 W C B a l a n c e 1 0 7 . 3 1 5 2 . 4 9 32.53

Total Input 255.86 408.12 411.22 334.56 Total Output 200.55 262.25 321.08 258.16 Total Balance 55.31 145.87 90.14 76.40

' (kg/ha/yr) SR Input 48.76 42.59 48.84 45.36 SR Output 6.02 6.16 6.56 5.83 SR B a l a n c e 4 2 . 7 a 36.43 42.28 39.53 A R Input 42.82 40.83 47.46 42.72 A R Output 8.46 8.73 8.37 8.51 AR B a l a n c e 3 4 . 3 6 32.10 3 9 . 0 9 34.22 W C Input 4 9 . 7 9 59.14 37.93 W C Output 11.75 4.45 5.45 W C B a l a n c e 3 8 . 0 4 54.69 3 2 . 4 8

Total Input 91.58 133.21 155.44 126.01 Total Output 14.48 26.64 19.38 19.79 Total Balance 77.10 106.57 136.06 106.22

(kg/ha/yr) SR Input 65.37 58.82 62.96 58.72 SR Output 162.55 165.51 174.21 160.41 SR B a l a n c e - 9 7 . 1 8 - 1 0 6 . 6 9 -712.25 -702.69 A R Input 61.12 56.76 58.85 52.35 AR Output 192.30 198.44 190.20 193.34 AR B a l a n c e -137.18 - 1 4 1 . 6 8 -732.35 -240.99 W C Input 76.11 80.52 52.08 W C Output 48.71 394.32 171.77 W C B a l a n c e 27.40 - 3 1 3 . 8 0 - 1 1 9 . 6 9

Total Input 126.49 191.69 202.33 163.15 Total Output 354.85 412.66 758.73 525.52 Total Balance -228.36 -220.97 -556.40 -362.37

( c o n t i n u e d o n next p a g e )

Nutrient Balances 77

Table 6.17 ( c o n t i n u e d )

Crop Flow

Cropping pattern0

Crop Flow SR/AR SR/AR/C SR/AR/P SR/AR/SP

Ca (kg/ha/yr) SR Input 157.74 155.05 146.61 154.54 SR Output 16.96 17.25 18.11 16.81 SR B a l a n c e 1 4 0 . 7 8 1 3 7 . 8 0 1 2 8 . 5 0 137.73 AR Input 148.58 134.08 138.89 112.49 AR Output 19.21 19.82 19.00 19.31 AR B a l a n c e 129.37 1 1 4 . 2 6 1 1 9 . 8 9 93.28 WC Input 141.02 150.60 99.98 W C Output 5.76 1.07 37.96 W C B a l a n c e 1 3 5 . 2 6 1 4 9 . 5 3 62.02

Total Input 306.32 430.15 436.10 367.01 Total Output 36.17 42.83 38.18 74.08 Total Balance 270.15 387.32 397.92 292.93

Mg (kg/ha/yr) SR Input 20.84 22.45 20.58 19.47 SR Output 11.02 11.24 11.88 10.79 SR B a l a n c e 9.82 1 1 . 2 1 8.70 8.68 AR Input 19.76 21.54 19.36 19.37 A R Output 13.95 14.39 13.80 14.02 AR B a l a n c e 5.81 7.15 5 . 5 6 5.35 WC Input 25.18 27.82 20.33 WC Output 8.45 3.36 0.00 W C B a l a n c e 16.73 2 4 . 4 6 20:33

Total Input 40.60 69.17 67.76 59.17 Total Output 24.97 34.08 29.04 24.81 Total Balance 15.63 35.09 38.72 34.36

S (kg/ha/yr) SR Input 38.22 31.34 37.53 36.68 SR Output 3.68 3.77 4.01 3.58 SR B a l a n c e 3 4 . 5 4 2 7 . 5 7 3 3 . 5 2 3 3 . 1 0 A R Input 32.40 29.82 36.79 35.16 AR Output 5.08 5.24 5.03 5.11 AR B a l a n c e 2 7 . 3 2 24.58 3 1 . 7 6 30.05 W C Input 6.62 7.52 4.80 WC Output 9.90 3.21 0.00 W C . . B a l a n c e - 3 . 2 8 4.31 4.80

Total Input 70.62 67.78 81.84 76.64 Total Output 8.76 18.91 12.25 8.69 Total Balance 61.86 48.87 69.59 67.95

a. SR - spring rice, AR - autumn rice, C - corn, P - Irish potato, SP - sweet potato, WC - winter crop.

78 Soils Under Stress

for Ca, 16-39 kg/ha/yr for Mg, and 49-70 kg/ha/yr for S. Po­tassium (K) is the only nutrient element that shows negative balances; the amounts vary from -228 kg/ha/yr for the double-cropped rice pattern to -556 kg/ha/yr for the two rice and potato cropping pattern.

Examination of the contribution of individual crops to the total balance of their corresponding cropping patterns reveals that for nitrogen (N), positive balances were obtained for spring rice when the yields were low, but slightly nega­tive balances were obtained for autumn rice when the yields were high. For other nutrient elements except K, all the crops contributed positively to the total balances. For K, both spring and autumn rice contributed to a negative balance about equally. Sweet potato gave a similar amount of negative bal­ance as the rice crop, but potato showed a much higher amount of contribution to the negative K balance. Corn was the only crop that gave a positive K balance, but because the amount was rather small, it could not offset the much higher negative balance from the rice crop.

The levels of nutrient balances, however, varied con­siderably among fields. Table 6.18 illustrates these variations for the individual nutrients.

We also calculated the balances of these nutrient ele­ments for the maximum and minimum yields, assuming that the amount of fertilizer input is the same and yield differ­ences are mainly attributable to weather conditions. The re­sults are presented in Table 6.19 in comparison with those obtained from actual yields in 1991. The patterns of nutrient balances are still the same as described earlier, except the amounts (whether positive or negative} are higher with the maximum yields and lower with the minimum yields.

SUSTAINABILITY In relating nutrient balance to long-term sustainability of land OF LAND productivity, the basic assumption is that a negative balance PRODUCTIVITY would indicate a loss of nutrient from the system. If the prac­

tice is continued over a long period, quality of the land will be degraded and, consequently, sustainability of land produc-

Nutrient Balances 79

Table 6.18 Distribution of fields with different levels of nutrient balances

Total balance Percent of fields3

Nutrient (kg/ha) SR/AR SR/AR/C SR/AR/P SR/AR/SP

N -98 to 0 11.4 0.0 II.1 9.1 Oto 75 57.1 0.0 29.6 40.9

75 to 150 28.6 42.9 44.4 45.5 150 to 225 2.9 57.1 14.8 4.5 225 to 300 0.0 0.0 3.7 0.0

P 0 to 60 30.0 0.0 0.0 18.2 60 to 120 64.3 71.4 44.4 59.1 120 to 180 5.7 28.6 44.4 13.6 180 to 240 0.0 0.0 7.4 9.1 240 to 300 0.0 0.0 3.7 0.0

K -768 to -600 0.0 0.0 33.3 0.0 -600 to -450 0.0 0.0 40.7 9.1 -450 to - 3 0 0 5.7 14.3 25.9 77.3 -300 to -150 85.7 71.4 0.0 13.6

-150 toO 8.6 14.3 0.0 0.0 Ca 0 to 200 51.4 0.0 11.1 22.7

200 to 400 31.4 71.4 59.3 54.5 400 to 600 12.9 14.3 18.6 13.6 600 to 800 2.9 14.3 3.7 9.1

800 to 1,420 1.4 0.0 7.4 0.0 Mg -25 to 0 11.4 0.0 0.0 0.0

0 to 25 65.7 42.9 14.8 40.9 25 to 50 22.9 14.3 66.7 45.5 50 to 75 0.0 42.9 14.8 1.6

75 to 100 0.0 0.0 3.7 0.0 S -5 to 40 18.5 14.3 14.8 18.2

40 to 80 64.3 71.4 59.3 54.5 80 to 120 11.4 14.3 18.5 18.2 120 to 160 5.7 0.0 3.7 9.1 160 to 200 0.0 0.0 3.7 0.0

No. of fields 70 7 27 22

a. SR - spring rice, AR - autumn rice, C - corn, P - Irish potato, SP -sweet potato.

tivity will be lowered. A positive balance may also affect land-use sustainability if the nutrient is accumulated to the level that it becomes toxic or creates a nutrient imbalance. There­fore, in assessing sustainability, we looked for nutrients that are likely to be continuously depleted or continuously accu­mulated.

The nutrient balance analysis previously discussed is not yet completed. It has not accounted for the inflow of

8o Soils Under Stress

Table 6.19 Total balances of nutrient elements at minimum, actual, and maximum yield levels for the different cropping patterns

Total balance (kg/ha)1

Nutrient Yield level 3 SR/AR SR/AR/C SR/AR/P SR/AR/SP

N Minimum 106.20 208.33 174.69 152.74 Actual 55.31 145.87 90.15 76.40 Maximum 7.44 97.14 22.25 19.86

P Minimum 80.69 114.01 141.06 112.13 Actual 7 7 . 0 9 106.56 136.05 106.22 Maximum 73.51 102.47 131.65 101.87

K Minimum -120.69 -111.68 -338.69 -180.45 Actual -228.36 -220.97 -556.40 -362.37 Maximum -283.80 -275.60 -679.22 -438.43

Ca Minimum 281.63 399.31 410.12 320.44 Actual 270.15 387.33 397.93 292.93 Maximum 265.34 382.54 392.67 283.77

Mg Minimum 22.67 44.18 46.99 41.58 Actual 15.64 35.08 38.71 34.35 Maximum J 0.84 30.07 33.19 29.40

S Minimum 64.09 54.52 72.82 70.24 Actual 61.85 48.86 69.60 67.96 Maximum 59.78 46.31 66.94 65.80

a. Actual yields in 1991 were obtained from interviews; minimum and maximum yields were from farmers' recollection. b. SR - spring rice, AR - autumn rice, C - corn, P - Irish potato, SP - sweet potato.

nutrients through sediments and rainwater, and the outflow of nutrients through leaching and drainage. In Nguyen Xa, the amount of nutrients flowing in with the sediments is estimated to be very small |see Chapter 4} and thus could be omitted. The estimated amount of nitrogen flowing in with rainwater would be at most 16 kg/ha/yr. This amount can be added to the N balances in the previous calculation, making them somewhat higher. As for the condition of the lowland paddy fields, leaching is expected to be small and could be neglected. The major factor that should be considered is drain­age, which should play a key role in balancing the nutrient elements in the system. The extent by which a nutrient cle­ment is lost through drainage, in turn, will depend on its nature in solubility.

Although all the nutrient elements except K show posi­tive balances in the foregoing initial analysis, N and S are

Nutrient Balances 81

soluble; thus, they are expected to be lost through drainage. P, Ca, and Mg are rather immobile and are expected to re­main in the fields. These three nutrient elements are likely to be accumulated if the current practices are continued over a long period. Accumulation of Ca and Mg, however, would be beneficial due to their benevolent effects and the low p H of the soils in Nguyen Xa. On the other hand, accumulation of P may have a negative effect in the long run, if its level becomes too high. The highly negative K balance is certainly affecting the sustainability of land productivity, as the analy­sis indicates a loss of this element from the fields. As ex­pected, the cropping patterns with root crops show the great­est negative K balance, with the rice-rice-potato reflecting a negative balance of some 500 kg/ha/yr. Even in the double-cropped rice pattern, K balance is also quite negative. A con­tinuous loss of K at such amounts yearly would definitely lower land productivity in the long run. This nutrient is surely of utmost concern to sustainability of the current crop pro­duction system in Nguyen Xa.

The foregoing analysis also suggests that a substantial surplus of nutrients is likely leaving the fields in drainage water, polluting the water source into which it flows. There­fore, it is imperative that further investigation be conducted to ensure the health and well-being of water consumers who reside downstream.

N O T E S

1 . Per sao, this is 300-500 kg manure, 6-8 kg urea, 15 kg superphosphate, and 3 kg K G .

1. According to Angladette U966, 208), rainwater deposits 16 kg of nitrogen per hectare at Hanoi.

3. Per sao, this is 300-500 kg manure, 4-5 kg urea, 10 kg superphosphate or NPK, and 3 kg KC1.

8i Soils Under Stress

Table A6.1 Nutrient concentration of outflow and inflow components

Nutrient

Component N P K Ca M g S

Outflow

Rice

Grain (%) 1.210" Q.Q941 0.539a 0.009b 0.087b 0.052b

Straw (%) 0.450b 0.030b 1.400b 0.160b 0.080b 0.020b

Corn

Grain (%) 1.538c 0.352c 0.264c 0.013c 0.132c 0.132c

Stover (%) 0.403a 0.080c 0.750c 0.095c 0.100c 0.125c

Potato

Tuber (%) 0.320a 0.012a 0.423" 0.007d 0.022d 0.02 l d

Vine (%) 0.300a 0.012" 0.150" N A N A N A

Sweet potato

Tuber {%) 0.012" 0.016" 0.398" 0.3 50e N A e N A

Vine {%) 0.300* 0.024" 0.830" N A N A N A

a flow

Urea |%) 45f — — — — — Superphosphate (%) — — 20f — 12f

Potassium chloride (%) — — 52.35f — — — Lime (%) — — 40' — — Compound fertil. (%) 12.008 4.90* 9.96* — — — Pig manure (kg/t) 3.256» 1.428" 3.734" 3.433h 1.529h 0.156h

Night soil (kg/t) 5.5003 1.7303 5.190" 6.8661 2.2941 0.234'

Azolla (kg/t) 2.250* • • • * •

Sources: a. Tran An Phoung, ed. 1990. Standard criteria for agriculture and food industry. Hanoi: Agricultural Publication House.

b. S. K. De Datta. 1989. Rice. In Detecting m i n e r a l n u t r i e n t deficiencies i n uopical and temperate crops. cd. D. L. Plucknet and H. B. Sprague. Tropical Agriculture Series, No. 7. Boulder: Westview Press. (Calculated at 13 and 50% moisture content for grain and straw, respectively.)

c. ). B. Jone and H. V. Eck. 1973. Plant analysis as an aid in fertilizing corn and grain sorghum. In Soil testing and plant analysis, ed. L. M . Walsh and J. D. Beaton. Madison, Wise: Soil Science Society of America. (Calculated at 12.1 and 50% moisture content for grain and stover, respectively.)

d. R. Kunkel, N . Holstad, and T. S. Russell. 1973. Mineral element content of potato plants and tuber vs. yields. A m e r i c a n Potato J o u r n a l 50:275-83.

e. W. A. Hill. 1989. Sweet potato. In Detecting m i n e r a l n u t r i e n t deficiencies i n tropical and temperate crops, ed. D. L. Plucknet and H. B. Sprague. Tropical Agriculture Series, No. 7. Boulder: Westview Press.

f. Standard nutrient contents of urea, superphosphate, and potassium chloride. g. Le Trong Cue, personal communication. Compound fertilizer commonly used in Vietnam is the 12-12-

UiN-PjCyKjO) formula. h. Calculated on the basis of the following estimates:

fresh pig manure contains 70% moisture content; of the solid part, 30% is pig dung and 70% is rice straw; pig dung contains 3.068% Ca and 1.325% Mg (dry wt.J (Ref. j); dry straw contains 0.32% Ca, 0.16% Mg, and 0.04% S (Ref. c}; S content in pig dung is twice that of rice straw.

i. Calculated on the basis of the following estimates: Ca content of night soil - twice of the Ca content of pig manure; Mg content of night soil - 50% more than pig manure; S content of night soil - 50% more than pig manure,

j. C. Duthion. 1980. Landspreading of liquid pig manure: i . Effects on yield and quality of crops. In Effluents f r o m livestock, ed. [. K. K. Gasser. London: Applied Science Publisher.

* Only nitrogen is considered an input to the systemi other nutrients are considered taken out from and recycled back to the system.

Subsidiary Enterprises and Their Effects on Agricultural Production

Although agriculture is their main occupation, most Nguyen Xa villagers are also engaged in subsidiary enterprises. These enterprises have generated good income to the villagers and have even become the major source of income for many households. In recent years, particularly after the change in government policy to the individual responsibility system, subsidiary enterprises in Nguyen Xa have increased substan­tially. Taxing policy also favors the development of subsid­iary enterprises as they are subjected to a much lower tax rate than agricultural production. The increase in subsidiary activities is expected to somehow affect agricultural produc­tion, which may also affect land-use sustainability in the long run. This section examines the subsidiary enterprises in Nguyen Xa and their effects on agricultural production.

A rapid rural appraisal technique was used in gathering information. Five households with different subsidiary en­terprises were interviewed in detail. Village-level data were obtained from interviews with Cooperative officers. Other farmers were also interviewed, and related information was gathered from researchers conducting other parts of the study. N o attempt was made in getting the details of all subsidiary enterprises in the village. Rather, the intention was to gather just enough information to assess the general effects of sub­sidiary enterprises on agricultural production and to project their consequences on land-use sustainability.

84 Soils Under Stress

S U B S I D I A R Y Subsidiary enterprises have long been a part of household E N T E R P R I S E S activities in every village in the Red River Delta. Tradition-IN N G U Y E N X A a j i ^ these enterprises are closely linked with agriculture.

Initially, leisure time was used to produce agricultural imple­ments for daily use or to process agricultural products for higher value. Later, these enterprises developed to a special­ized level, as certain villages became well known for certain enterprises. Nevertheless/ villagers st i l l consider them as supplementary activities and do not separate them from ag­riculture. The saying, "With water buffaloes in the fields, they are keen cultivators, while next to the forge or pottery ki ln , they are skil l craftsmen," clearly illustrates the dual characteristics of rural villagers in the region. With increas­ing population and scarcity of cultivated land, subsidiary enterprises began to play a more important role in village life and became an essential part of the villagers' survival strat­egy in the Red River Delta. It is not surprising that subsid­iary activities in the delta villages have increased over the years, and more so in recent years, in response to the incen­tive provided by the new government policy.

Nguyen Xa is no different from other villages in the Red River Delta with regard to the trend in subsidiary enter­prises. Nguyen Xa, which is ideally located near the main road and not far from the district and provincial towns, is perhaps among the front-runner villages in the delta in de­veloping subsidiary enterprises. Nguyen Xa villagers are con­sidered "half agriculturist/half trader" [ b a n n o n g b a n t h u o n g ) . Although crop cultivation in the village is highly intensified and Nguyen Xa farmers are experienced rice cultivators, sub­sidiary enterprises in the village continue to develop with strength. There are now a wide variety of subsidiary enter­prises, from making sweets, liquor, pressed ham, and tofu to dealing junk and scraps (copper, lead, aluminum, glasses, plas­tic). Others are construction, carpentry, rice milling, glass manufacturing, and motorized transporting of goods. In 1991, of the 1,625 households presented in the village, 1,200 house­holds (73.85 percent) were engaged in subsidiary enterprises. The percentage of households engaged in subsidiary activi-

Subsidiary Enterprises 85

ties, however, varied among the different hamlets. Bac Lang Hamlet had the highest percentage (96 percent], while Tran Phu Hamlet had the lowest percentage (30 percent}.

Subsidiary production is organized in different forms. Production is more specialized for those with greater capital. Raw materials are delivered, and finished products are picked up by others to be sold. Households of this type account for 20 percent of total households engaging in subsidiary enter­prises. The second group consists of those who both produce and sell their products. This group of households has less capital than the first group. They make their products at night, sell at the market in the morning, and work in the paddy in the afternoon.

Subsidiary enterprises are closely linked with the v i l ­lage marketing system. Previously, Nguyen Xa had three main market days per month. Currently, the market meets daily without differentiating between major and minor days. People from surrounding villages also come to Nguyen Xa market to sell many types of goods and purchase local products such as sweets, ham, and soft drinks.

A study of the handicraft industry indicated that in 1989, the value of output reached 855 mill ion d o n g , of which fam­ily production claimed 673.4 million d o n g (78.7 percent). From 1990 to 1991, subsidiary enterprises in Nguyen Xa ex­pended 400 tons of rice, 100 tons of soybean, and 80 tons of meat. Individual families engaged in subsidiary enterprises earned 1,095 million d o n g , 94 percent of the total value, whereas collective subsidiary activities claimed a modest 6 percent.

I N C O M E F R O M Subsidiary enterprises provide a significant amount of in-S U B S t o i A R Y come to the village households. In fact, earnings from sub-E N T E R P R I S E S sidiary enterprises have become the major part of household

income for many households. Table 7.1 presents the income, ranging from 30 to 77 percent, from different sources of five families that we interviewed. Income from subsidiary activi­ties has allowed these households to acquire better housing,

86 Soils Under Stress

Table 7.1 Income from different sources of five selected households in Nguyen Xa

Head of household Occupation

Gross income

(mil. dong)

Income source (%J

Crop Animal Subsidiary production production enterprise

Mr. Luyen Rice farmer, sweets and soft-drink producer 5.97 9.15 22.51 68.34

Mr. Tru Rice farmer, alcohol and tofu producer 10.53 29.63 29.25 41.12

Ms. Mui Rice farmer, miller 18.17 6.42 16.53 77.05 Mr. Vuong Rice farmer, scrap dealer 5.56 36.59 12.19 51.22 Mr. Ngu Rice farmer, "da" cake

producer 4.82 22.70 47.10 30.29

cleaner and safer water sources, more appliances, and mate­rial comforts.

The role of subsidiary enterprises in family life, as well as how they are integrated in daily household activities, is presented in the following three household case examples:

• The first case is the family of Mr. Luyen in Bac Lang Hamlet. His family consists of seven. However, only one main laborer cultivates the fields with a total area of 4 sao and 10 t h u o c (1,680 m1}. The subsidiary work of this family is producing soft drinks during the hot season (from the third to the seventh lunar month] and producing sweets for the rest of the year. Subsidiary activity begins at 4 A . M . and ends at 10 A . M . After the products are picked up by buyers, the family eats lunch, then works in the cultivated fields in the afternoon. One batch of soft drinks (2,500 liters] requires 50 kg sugar and 100 kg rice malt. One batch of sweets (pea­nut candy and "cay" cake) uses 500 kg sugar, 500 kg malt, and 800 kg peanuts. Raw materials are delivered and final products are picked up at his home. After sub­tracting production costs and living expenses, his fam­ily saves 3 million d o n g annually from these subsid­iary enterprises. The amount equals to 2.5 tons of rice grain. In addition, subsidiary income has enabled his family to raise two litters of sow and two pigs per year.

Subsidiary Enterprises 87

The pigs provided him with 5 tons of manure per year and an income of 1.2 mil l ion d o n g from their sale.

• The second case is the family of Ms. M u i in Hong Phong Hamlet who has a rice mi l l . Her rice mi l l has the ca­pacity to dehull 10 tons of paddy per day. Her daily in­come ranges from 20,000 to 100,000 d o n g . Customers who want the husk are charged 300 d o n g per 10 kg paddy. Those who do hot, pay 250 d o n g per 1 o kg paddy. She informed us that if the machine uses 20 liters of gasoline, which cost 50,000 d o n g , she collects 120,000-140,000 d o n g . Her family has 6 sao (2,160 m2) of con­tract paddy fields. Although three crops can be grown in these fields, she rarely plants the winter crop. If the weather is favorable, she plants 3 sao of sweet potato for pig feed. Her household raises five to six pigs during the year. The average out-of-pen weight is 100 kg per pig. Feed for pigs primarily consists of rice bran and other by-products from the rice mi l l . After deducting all the expenses (tax, irrigation fee, fertilizer, pesticide, wages}, her profit from rice cultivation in 6 sao fields is about 1 ton of paddy per year. This profit is equal to the income earned from running the rice mi l l for only thirty days. We asked her why she continued rice cultivation when it provided such a poor income. She replied, "I am a farmer, my ancestors were farmers; rice cultiva­tion is our flesh and blood, and I cannot live without it."

• The third case is Mr. Vuong's household who lives in Le Tien Hamlet. His subsidiary work is scrap-dealing. When we arrived at his house for the interview, his entire family was outside in the courtyard separating copper and aluminum scraps, duck feathers, and bro­ken glasses. His household has seven members, two of whom are primary laborers in cultivating 8 sao (2,880 m1) of paddy fields. After deducting taxes and other ex­penses, the rice remaining is not sufficient to meet his household demands. He supplements his agricultural

88 Soils Under Stress

income by scrap-dealing. He buys by bulk from smaller dealers, separates the different types of scraps, then re­sells them to various places. Scrap-dealing requires little starting capital, has a high profit margin, and is not taxable. For smaller dealers, their capital is simply a piece of candy. They travel throughout the vicinity and exchange candy with children for scraps such as cop­per, lead, aluminum, glass, nylon, and chicken and duck feathers. People often describe scrap dealers as b u o n t h a t n g h i e p , n g u q u a n v i e n ("looking like a beggar, but living like a royalty"). We observed that Mr. Vuong's home is spacious, well decorated, and filled with mate­rial comforts.

E F F E C T S OF

SUBSIDIARY

ACTIVITIES

ON AGRICULTURE

Information obtained from interviewing a number of villag­ers revealed that subsidiary activities in Nguyen Xa Village have both positive and negative effects on agricultural pro­duction. On the positive side, income earned from subsid­iary enterprises was used to purchase farm equipment, new seed varieties, fertilizers, pesticides, and animal feed, pro­viding more input to agricultural production. Several farm­ers indicated that income from subsidiary activities has en­abled them to maintain or even increase pig raising. Pigs, in turn, have helped to maintain the supply of manure for crop production. Our study showed that 3 percent of households with subsidiary work raise ten pigs per year; 15 percent, four to five; and 82 percent, two to three.

The negative effect was the competition for labor be­tween subsidiary activity and crop cultivation. Households with subsidiary activities indicated that they spent less time of their family labor on crop cultivation but used hired labor­ers instead. With this arrangement, labor input to crop culti­vation is still maintained. However, households with a con­siderable amount of subsidiary activities tended to give up planting of the third crop, as illustrated in the case of Ms. M u i . In all instances, rice cultivation is still considered an important enterprise that has to be maintained.

Subsidiary Enterprises 89

CONCLUSION Subsidiary enterprises clearly play an important role to the livelihood of Nguyen Xa villagers. They generate income for daily expenses of farmers; for housing and material comforts; for agricultural taxes, irrigation fees, and other contributions,-for new agricultural equipment and materials; for seeds of new and improved varieties; and for feed and other input to animal husbandry. For many households, income from sub­sidiary activities has become the major pan of family income. Nguyen Xa has no more land to further expand for crop cul­tivation. Agricultural production is currently highly intensi­fied, and crop yields have already been high. Thus, only little room is left for further increase in agricultural production. With a continuing increase in population and the demand for better living standards, subsidiary activities may be the only way out.

Although subsidiary enterprises have some effects on agricultural production, the effects are more positive than negative. So far, subsidiary enterprises have no negative ef­fect on land-use sustainability. In fact, they have helped main­tain or have even increased the inflow of nutrients to the fields (through manure and fertilizers), which, in turn, have helped sustain the productivity of the Nguyen Xa land re­source. How long this situation lasts w i l l depend on the vi l ­lagers' attitude. Currently, the villagers still have a high re­gard for agriculture, particularly rice cultivation (and pig rais­ing as it provides manure for rice cultivation), as it has long been a part of their life. The overall economic development of Vietnam is expected to be rapid, and great opportunities for expanding subsidiary enterprises can be anticipated. The changes in economic environment and alternative opportu­nities wi l l certainly affect the villagers7 attitude toward agri­culture. It is difficult to predict how fast the changes in eco­nomic environment wi l l take place and subsequently how the changes wi l l affect farmers' attitude. Nevertheless, it is unlikely to happen in Nguyen Xa in the near future.

CHAPTER 8

Goro Uehara Aran Patanothai

Potential for Further Increase in Agricultural Production

In the 1930s, when the population density of Thai Binh Prov­ince was nearing 500 persons/km2, Pierre Gourou (1936), a French scholar, was speculating that the region had nearly reached its human carrying capacity. In 1992, some sixty years later, the population has more than doubled in the province and tripled in Nguyen Xa Village. Evidently, the French scholar underestimated the area's carrying capacity, because he could not foresee how agricultural production on an al­ready tightly managed and apparently fully utilized land could keep pace with population expansion. But since Gourou made his first forecast, better water control, new varieties, mul­tiple cropping, and high chemical input have enabled pro­ductivity to increase at a higher rate than population.

Today, an outsider visiting Nguyen Xa for the first time would be compelled to ask the same question raised by Gourou in the 1930s. The question is especially pertinent now because even if the village succeeds in attaining its goal of lowering the population growth rate to 1.5 percent, the number of people in Nguyen Xa would double in about fifty years. Can the villagers continue to expect productivity to keep pace with population growth, or has the land's carrying capacity been finally reached? This part of the study attempts to answer this question.

P O T E N T I A L F O R As indicated in Chapter 1, all the lands in Nguyen Xa arc I N C R E A S E IN C R O P already in use. After Directive 10 was put into effect, even P R O D U C T I O N 0]<j Cooperative stables, playgrounds, and grave mounds were

converted to cultivated fields. In short, no more land can be

92 Soils Under Stress

cultivated. Furthermore, essentially all the cultivated land is already grown to two crops of rice. Thus, a further increase in crop production must come from raising crop yields or increasing a fraction of the land used for the third crop.

P O T E N T I A L F O R I N C R E A S I N G A R E A O F T H E THIRD C R O P

In 1992, the third crop in Nguyen Xa covered about 40 per­cent of the cultivated land. Fields suitable for growing the third crop are those located in relatively high spots, as low-lying fields generally are prone to water stagnation. Farmers interviewed stated that all the suitable land for growing the third crop had already been used. A further expansion would lead to crops grown under marginal and unprofitable condi­tions. Furthermore, subsidiary enterprises in the village are increasing. These enterprises, which provide good income to the farmers, result in less attention being given to the culti­vation of the third crop (see Chapter 7). Under these condi­tions, the potential for further expansion of the third crop area is also small.

P O T E N T I A L F O R I N C R E A S I N G C R O P Y I E L D S

Rice is the crop of most concern, as Nguyen Xa villagers de­pend on this staple. For the past five years (1987-91), village rice yields have fluctuated between nine and ten tons per hectare per year with no indication of an upward trend. Is this yield plateau only temporary, or is it an indication of the end of the green revolution for Nguyen Xa? One indication of the permanence of the situation can be inferred from cur­rent rice yields. Few places in the world produce nine to ten tons of rice each year per hectare of land. Evidently, the farm­ers of Nguyen Xa have already adopted most, if not all, of the practices of the green revolution, including the short-strawed, early maturing varieties with erect leaves, high crop protec­tion and fertilizer input, and good water control that allow the new varieties to attain high yields.

To explore the possibility for further yield increase,

Increasing Agricultural Production 93

potential yields for the spring and autumn crops of the most popular rice variety, CR203, were estimated by simulation, using the CERES-Rice Simulation Model (Godwin et al. 1990). This simulation model is included in a computerized deci­sion-support system (Jones 1993), which enables the user to simulate the growth, development, and yield of a particular cultivar of rice in any rice-growing area of the world. The software allows the user to choose the cultivar, planting data, plant population, row spacing, the timing, rate, and depth of nitrogen fertilizer application, and the amount and timing of irrigation water application. In order to simulate the growth and development of rice variety CR203, it was necessary to find a genetically similar variety from our database. It turned out that CR203 is genetically related to IR64, a variety widely used for breeding in the national agricultural research centers.

To simulate the growth and development of CR203 in Nguyen Xa, the genetic features of IR64, along with daily weather data collected in Thai Binh Province from 1982 to 1991, were used as inputs to the model. To mimic farming conditions in Nguyen Xa, 30-day-old seedlings of variety CR203 were transplanted in mid-February and again in mid-July on a well-watered, fully fertilized, deep, silty clay loam soil. These conditions were selected to mimic situations in which weather is the only factor limiting the performance and yield of the cultivar. These are often referred to as "maxi­mum yield experiments."

Tables 8.1 and 8.2 compare observed and predicted yields for the spring and autumn crops of the rice variety CR203 in Nguyen Xa during 1982-91. The results indicate that the farmers of Nguyen Xa are obtaining yields equaling 80 per­cent of the maximum. A major part of the yield gap can be attributed to yield losses from insect, disease, bird, and ro­dent damages. However, farmers in Nguyen Xa already use modern pesticides for crop protection and are probably achiev­ing near optimum plant protection with the chemicals cur­rently available. Some improvements might be possible on fertilizer management, but it is not likely to be economically feasible to narrow the yield gap much further. Apparently, in

94 Soils Under Stress

Table 8.1 Comparison of observed and predicted heading date, maturity date, and grain yields for the 1 9 8 2 - 9 0 spring rice crops transplanted on 15 February (day 46)

Heading date3 Maturity date Grain yield (kg/ha)

Observed 133 (12 May) 167 (15 July) 5,400 (79% of predicted) Predicted

1982 141 173 6,974 1983 142 174 7,137 1984 141 173 6,503 1985 139 171 6,883 1986 139 171 6,883 1987 127 160 6,456 1989 138 171 7,146 1990 136 169 6,978

Average 137.9 (17 May) 170.3 (18 June) 6,870

Observed Predicted

Days to heading 133-46 -87 138-46-92 Days to maturity 167 - 46 - 121 170 - 46 - 124 Yield/day/ha 5400/121 - 44.6 6870/124 - 55.4

a. "Heading date" means when panicles emerge.

Table 8.2. Comparison of observed and predicted heading date, maturity date, and grain yields for the 1 9 8 2 - 9 1 autumn rice crops transplanted on 15 July {day 197)

Heading date Maturity date Grain yield (kg/ha)

Observed 258 (14 Sept.) 288 (14 Oct.) 4,590 (83% of predicted) Predicted

1982 262 292 5,412 1983 260 294 5,386 1984 263 301 4,535 1985 262 296 5,492 1986 262 298 5,390 1987 260 294 6,500 1988 260 297 5,026 1989 260 296 6,174 1990 260 294 5,711 1991 259 292 5,488

Average 260.8 (17 Sept.) 296.0 (22 Oct.) 5,511

Observed Predicted

Days to heading 258 - 197 - 61 261 - 197 -64 Days to maturity 288- 197 -91 296- 197 -99 Yield/day/ha 4590/91 -50.4 5511.4/99-55.7

Increasing Agricultural Production 95

Nguyen Xa the opportunity to increase productivity through adoption of modern technologies has nearly been exhausted.

When asked to identify ways to increase yields, Nguyen Xa farmers most frequently cited new varieties as the factor most likely to enable production to keep pace with popula­tion growth.

P O T E N T I A L

F O R I N C R E A S E

IN A N I M A L

P R O D U C T I O N

The Nguyen Xa agricultural system is focused on rice pro­duction. Animal husbandry serves as a complementary and suplementary activity to rice production. Hogs are the prin­cipal livestock kept in the village. Pigs are raised primarily to produce manure for rice cultivation, although meat is con­sumed and used in making meat .products as a subsidiary enterprise. Most families keep two to five pigs ; only a few keep more than five pigs. Farmers indicated that pig raising resulted in little or no profit, but they continued to raise them for the value of the manure for rice production.

Farmers also keep buffalo and cattle, but primarily as draft animals. Despite the need for draft power, the number of buffalo has been declining. Currently, the village has a shortage of draft animals, and most households share a buf­falo. The main reason for the declining number of buffalo and cattle is lack of feed, as essentially all the land is used continuously for crop cultivation.

Farmers generally keep a few chickens, and some house­holds raise ducks. There are also a few pigeons, but no other type of poultry was observed. These animals are raised pri­marily for home consumption, and the potential for an in­crease in production is rather small.

Although Nguyen Xa has many ponds, fish culture is not as intensive as one would expect. This is partly because ponds are used for many purposes, including bathing and washing, cultivating aquatic weeds to feed pigs, and for cul-turing fish. The multiple uses of ponds constrain fish cul­ture since the usual practice of adding manure to the ponds for fish culture reduces water quality for domestic uses. Large ponds are also shared by a number of households, making

96 Soils Under Stress

management of fish culture more complicated. Although there is considerable scope for increasing fish culture, the constraints w i l l make it difficult in practice. However, a greater potential for fish culture appears to be in the irriga­tion canals, as has been done by one farmer in the village.

C O N C L U S I O N The foregoing analysis indicates that crop production in Nguyen Xa is nearly reaching its biological l imit . There is no more uncultivated space, and the available land has been used almost to its maximum intensity. The rice yields have pla-teaued and are not likely to increase in the near future, and there is very little room for further yield increase by improv­ing crop management. A substantial yield increase wi l l likely come from genetic improvement of rice varieties for higher yield potential. Yields wi l l undoubtedly increase in the de­cades ahead, but there are serious doubts about whether yields can be doubled to satisfy food demand for the anticipated population of the next fifty years. The possibility for increas­ing animal production is also limited, although some exist for fish culture. In places like Nguyen Xa, where modern agricultural methods are fully used, a new approach to food production wi l l need to be invented.

Nguyen Xa, as it exists today, serves as a microcosm of the world in fifty years. Nguyen Xa villagers, however, w i l l have the option to move to less populated regions or take up nonagricultural vocations. If world population doubles in the next fifty years, those options may no longer be available to most people. For this reason alone, Nguyen Xa deserves to be closely monitored over the coming decades.

Land-Use Sustainability

Nguyen Xa Village is a classical case of intensive manage­ment of natural resources, particularly the land resource, to meet the needs of human population. From a production view­point, Nguyen Xa represents a success story. Through im­provement of water control by constructing an extensive ir­rigation system, intensive cropping, and use of improved crop varieties, manure, fertilizers, and other crop management practices, Nguyen Xa farmers have been able to increase pro­duction sufficiently to cope with increased population. Over the past fifty years, while population has tripled, rice yield has increased nearly fivefold. The current rice yield is at 9-10 t/ha/yr. Not many places in the world have achieved this level of yield. Population pressure has been a major driving force in the effort to obtain such a high production level. The change in land-use policy by the government also provided a favorable incentive.

Such an achievement has not been attained without a price. Farmers have worked very hard, placing immense ef­forts in managing the crops properly and in a timely fashion. Perhaps most important in the long run is the degradation of natural resources as a consequence of overuse. As crop yields increase and crop cultivation becomes more intensified, pres­sure is increasingly put to the land, the resource that is al­ready severely limited. The question that faces us now is, How much longer can the land resource stand such a high pressure? In other words, is the quality of the resource base being maintained? Evidence from elsewhere in Southeast Asia indicates that land as intensively cropped as that of Nguyen Xa's paddy fields tends to suffer serious yield decline within ten years (Multiple Cropping Project 1980}. Wi l l this possibly

98 Soils Under Stress

happen in Nguyen Xa as well? As population in Nguyen Xa continues to increase, the demand for food wi l l certainly in­crease. How much more production can the land support? These sustainability questions are of prime concern in this study. This chapter presents a synopsis of major findings that have been discussed in detail in earlier chapters.

Q U E S T I O N O F

F U R T H E R

I N C R E A S E

IN P R O D U C T I O N

With everything done manually, the agricultural production system of Nguyen Xa may appear underdeveloped superfi­cially. However, a close examination wi l l reveal that the sys­tem is actually a high technology production system, and just about every aspect of modern production technology (high-yielding varieties, manure, green manure, chemical fertilizers, pesticides) is employed. Furthermore, much local knowledge have developed through experiences over genera­tions. The combined local knowledge and modern technolo­gies have enabled Nguyen Xa farmers to achieve a remark­ably high level of production. Results from our crop simula­tion indicate that the current rice yield in Nguyen Xa has already reached 80 percent of its maximum potential. How­ever, the estimated potential yield is based on the assump­tion that there is no limiting factor except weather condi­tions. In reality, everything is unlikely to be perfect, even under the best management possible. Thus, the maximum yield that could actually be realized would certainly be lower than that simulated (i.e., very little room is left for further yield improvement by cultural management). The results of our investigation on soil parameters and nutrient balance analysis indicate some possibilities for improvement by fer­tilizer management, but their economics are still question­able. Apparently, the opportunity to increase production through adoption of modern technologies has nearly been exhausted. Significant yield increases wi l l depend on genetic breakthrough in improving rice crop varieties, which is un­foreseen in the near future.

Currently all village lands have already been used. Even old stables and graveyards have been converted to produc-

Land-Use Sustainability 99

tion fields. Essentially all paddy fields have been planted to two crops of rice. Although the third crop currently covers about 40 percent of the paddy land, it has occupied most, if not all, of the suitable fields. Further expansion wi l l lead to crops that are grown under marginal and unprofitable condi­tions. Besides, spaces are needed to multiply azolla for the spring rice crop. With increasing opportunities for subsidiary activities, growing the third crop becomes the less preferred alternative. Therefore, the potential for further increase in cropping intensity is virtually very low.

The possibility for increasing animal production is also limited. Buffalo and cattle are decreasing due to lack of graz­ing area and fodder. Pig raising, although unprofitable, is be­ing maintained because of the need for manure. There ap­pears to be a considerable potential for increasing fish pro­duction in the ponds, but their multiple uses and multiple sharing make it difficult in practice. Some possibilities exist for increasing fish production in the irrigation canals where fish raising can be accommodated.

Thus, our investigation points out that production of the Nguyen Xa agroecosystem is nearly reaching its biologi­cal l imit. The system appears unable to support a much larger population. Therefore, other alternatives wi l l need to be found to cope with increasing population.

Q U E S T I O N O F

L A N D Q U A L I T Y

D E G R A D A T I O N

With an elaborate system of nutrient recycling (just about everything possible is recycled back to the fields) and supple­mental application of chemical fertilizers, the land in Nguyen Xa appears to have been managed properly and efficiently. The land seems capable of supporting a high level of produc­tion over an extended period.

Our investigation, however, reveals that Nguyen Xa soils are not without problems. The soil analysis of 1992 in­dicates that currently most of the fields are high in acidity, more so in certain spots where there may be a buried acid sulfate layer. Evidence shows that soil pH has been declining, despite the common application of lime and the neutralizing

IOO Soils Under Stress

effects of irrigation water. Heavy application of manure and night soil, which have a positive effect in increasing the level of organic matter, might have contributed to the declining level of soil pH. Our nutrient balance analysis also indicates a considerable amount of surplus P that might be accumu­lated. Soil analysis, on the contrary, shows a decreasing trend of available P. However, it is possible that P accumulation might be in a nonavailable form, which would not be indi­cated by soil analysis. Nonetheless, these results suggest that the use of P to support crop growth in Nguyen Xa soils might be inefficient. Nutrient balance analysis also indicates a sub­stantial amount of K deficit. Although changes in exchange­able K over time could not be examined, the currently low level of K in all the fields suggests that this nutrient element might have been continuously depleting.

Apparently, despite good soil management in Nguyen Xa, soil quality is declining. If the current practices continue, sustainability of soil productivity in the long run w i l l be threatened. Soil acidity management wi l l play a key role in improving land quality. Although improving the management of P also deserves attention, depletion of K should be of most concern to the sustainability of land productivity in Nguyen Xa.

Beneficial effects of the current practices are also evi­dent. The increased level of organic matter indicates that soil structure has improved. The positive balances of all the nutrients (except K) suggest that the supply of these nutri­ents is sufficient to crop requirements. Accumulation of sur­plus Ca and M g also wi l l have a beneficial effect, because of the low pH in the soils. The question concerning land-use sustainability is whether these beneficial conditions can be maintained in the long run.

The situation is unlikely to be the same in the future. The population wi l l continue to increase and the demand wi l l increase, not only for food but also for other material comforts currently considered unnecessary. The open mar­ket economy to which Vietnam is now turning, the expan­sion of nonagricultural sectors, the improvement of infra-

Land-Use Sustainability 101

structures, and the government development policies all wi l l affect the farmers' soil management decisions directly or in­directly. Although it is difficult, if not possible, to predict what changes wi l l occur, their effects on land-use sustain­ability can be postulated by examining the likely changes in nutrient input and output parameters at the field level.

From the nutrient balance model presented in Chapter 6 (Figures 6.4 and 6.51, the inflow of nutrients is through rain, sediment, manure, night soil, azolla, and chemical fertilizer and lime. The outflow is through crop removal (grain and straw for rice, and tuber and vine for potato and sweet po­tato), leaching, and drainage. Maintaining sustainability of land productivity is, in essence, maintaining the balance of nutrient inflows and outflows.

In the future, the amount of nutrients flowing in with rain wi l l remain the same. The construction of the dike and irrigation system has brought flooding under control, which has greatly reduced the flow of sediments into the fields of Nguyen Xa. The inflow of sediments is expected to remain more or less the same in the future. The amount of night soil is not expected to change much, unless there is a substantial change in living conditions that lead to a change in farmers' attitude toward the use of night soil. Azolla production had substantially declined at one time because of a misunder­standing by farmers on azolla's effect on the rice crop in rela­tion to cold weather. However, production is increasing and is likely to be maintained, at least in the near future. The key components for possible changes are manure and chemi­cal fertilizers (including lime), which constitute the major inflow of nutrients.

The outflow through leaching is also expected to re­main constant. The outflow through drainage wi l l depend on the amount and kind of input and the nutrient surplus. With wet rice cultivation, drainage management is not ex­pected to change much from the current practice. An increase in outflow through grain and tuber would be desirable, and presumably wi l l be so with the increasing demand from in­creased population. Correspondingly, there wi l l be an increase

i o i Soils Under Stress

in outflow through rice straw and root crop vine that are re­moved from the fields. Currently, these straw and vine are recycled back to the fields through manure compost. If this recycle chain is broken, there wi l l be a big loss of nutrient inflow to the system.

Manure production depends almost entirely on pig rais­ing. Apparently, pig raising plays a key role in nutrient recy­cling. Any change that could cause a decrease in this enter­prise wi l l also break the nutrient recycling pathway and could pose a threat to long-term sustainability of the land resource. Some farmers have already complained that their pig raising operates at a loss, except for the value of manure gained for crop production. If the cost (feed and labor) of pig raising rises or the sale price of pork or pig falls, this could decrease the value of pig raising to farmers sufficiently for them to cut back on this activity, despite their need for manure. This situation is of great concern to land-use sustainability, and every attempt should be made to maintain pig raising. The changes in economic environment could discourage farmers to continue pig raising. If that happens, a means to com­pensate for the loss of nutrient inflow should be sought to maintain the balance and to maintain the sustainability of land productivity. Developing a new pathway to recycle rice straw and root crop vine to the fields would be an appropri­ate strategy.

Previously, with assistance from the Soviet Union, the price of chemical fertilizers in Vietnam was relatively inex­pensive. However, the cutback of Soviet assistance has made chemical fertilizers more costly, and the cost is expected to increase further. Experiences elsewhere in Southeast Asia have shown that small farmers generally are unable to afford a high application rate of chemical fertilizers. If manure pro­duction could not be maintained, the long-term sustainabil­ity of land productivity wi l l certainly be threatened.

Although land in Nguyen Xa appears to have been well managed, soil quality degradation may likely occur, threat­ening long-term sustainability of land productivity. Careful scientific monitoring is needed to make timely corrections.

Land-Use Sustainability 103

The nutrient balance analysis also points out a possi­bility of a negative side effect on water pollution resulting from removal of excess nutrients through drainage water. Although not related to land-use sustainability, this occur­rence would be harmful to the people residing downstream and therefore deserves further investigation.

DEVELOPMENT The foregoing discussion points out that little land is left for ALTERNATIVES further increase in production and that maintenance of soil

quality to sustain a high level of production, although it cur­rently can be achieved, w i l l be much more difficult in the future. What then would be the alternatives for future devel­opment of a place like Nguyen Xa?

Population control certainly deserves a high priority, and government programs are already in operation with con­siderable success. But even if the population growth rate is reduced to 1.5 percent (compared to 1.77 percent during 1985-90), the village population wi l l increase by 35 percent in twenty years. Encouraging out-migration also offers a quick and effective solution to the problem of overpopulation. The Vietnamese government has sponsored several large-scale programs to resettle people from the Red River Delta to the Midlands and mountains in the northwest. But the resettle­ment program is costly, and a new suitable site for resettle­ment is difficult to find. Expansion of employment opportu­nities in urban centers may offer a more viable alternative to resettlement in marginal areas.

Despite government efforts, population increase in the delta area still remains real. It wi l l be many years before the population growth rate can be brought to a halt. What devel­opment strategy would enable an already densely populated village like Nguyen Xa to accommodate more people and yet improve their living standards?

Our investigation showed that although agriculture is the main occupation, many households in Nguyen Xa are also engaged in subsidiary enterprises ranging from making sweets, liquor, pressed ham, and tofu ; dealing junk and scraps;

IO4 Soils Under Stress

working in construction, carpentry, rice mills , and glass manufacturing; to transporting goods by motorized vehicles. These activities have been increasing and have generated good income to the villagers. In fact, income from subsidiary ac­tivities has become the major part of family income for many households. These subsidiary activities, however, affect ag­riculture more positively than negatively. Positive effects are more investment in pig raising and in input for crop produc­tion, whereas negative effects are less time spent on crop production and a declining interest in growing the third crop. Subsidiary activities have actually helped to maintain or even increase the inflow of nutrients to the fields, which conse­quently sustain productivity of the Nguyen Xa land resource. With little room left for improvement in agriculture, subsid­iary activities may be the only alternative for coping with increasing population in the long run.

APPENDIX A

Workshop Participants

Center for Natural Resources Management and Environmental Studies, Hanoi University, Vietnam

Dr. Le Trong Cue Miss Nghiem Phuong Tuyen Mr. Pham Van Phe

Chiang Mai University, Thailand

Dr. Rojaree Netsangtip

Program on Environment, East-West Center, Honolulu, U S A

Miss Ton N u Vy

Hanoi Agricultural University, Vietnam

Dr. Dao Chau Thu Mr. Nguyen Van Hoan Mr. Pham Tien Dung Mr. Tran Danh Thin Mr. Tran Due Vien

Khon Kaen University, Thailand

Dr. Aran.Patanothai

University of Hawaii at Manoa, Honolulu, U S A

Mr. Keith Fahrney Dr. Harold J. McArthur, Jr. Dr. Goro Uehara Dr. Russell S. Yost

APPENDIX B

Workshop Schedule

Rural Resource Management in the Red River Delta of Viet­nam: A Case Study on Land-Use Sustainability in a Highly Intensive Cultivation and Densely Populated Area in Hanoi and Thai Binh Province, 11-30 June 1992

June

10 Visiting scientists of preparation team arrive in Hanoi

11-13 Planning meeting and examination of available data

14 Travel from Hanoi to Thai Binh; meet with province officials

15-16 Field research

17 Field research; additional visiting scientists arrive in Hanoi

18 Field research; additional visiting scientists arrive in Thai Binh

19 Field research

20-28 Field research, data analyses, group discussions, and preparation of group reports

29 Travel from Thai Binh to Hanoi

30 Wrap-up meeting at Center for Natural Resources Management and Environmental Studies, Hanoi University

July

1 Visiting scientists leave Hanoi

APPENDIX C

Questionnaire

Sustainable Land-Use Case Study of Nguyen Xa Village

PART 1 (one for each household) HOUSEHOLD

Interviewer no Name DATA

1. Household no Hamlet [ ]

2. Number of persons in household [ ]

Sex Working in the farm Person (M = male Age (MT = most of the time no. F = female) (years) ST = sometimes)

I ( ) M ( )F ( ) M T ( 1ST 2 ( ) M | )F ( ) M T ; )ST

3 ( ) M | )F ( ) M T ( )ST

4 ( ) M ( )F I ) M T : )ST

5 ( ) M ( ) F ( ] M T )ST

6 ( ) M I )F ( ) M T ( )ST

7 ( ) M I ) F ( J M T )ST

8 ( ) M | )F ( ) M T J ST

9 ( ) M | }F ( ) M T )ST

10 ( ) M | | F ( ) M T | S T

II ( ) M | )F I ) M T : JST

12 ( | M | I F ( | M T )ST

13 ( ) M | )F ( ) M T JST

14 ( ) M ( )F 1 | M T )ST

15 ( ) M | IF I ) M T 1ST

The interview was done with person no

3. Total number of farm laborers in household | ]

4. Number of fields that the household operates [ J

n o Soils Under'Stress

no. Sao T h u o c Cropping pattern*

1

2

3

4

5 6

7 8

9 10

11

12

'Write down the crops grown in each field in a year, beginning with the spring crop

SR/AR = Spring rice/Autumn rice SR/AR/SP = Spring rice/Autumn rice/Sweet potato SR/AR/P = Spring rice/Autumn rice/Potato S R / A R / C = Spring rice/Autumn rice/Corn SR/AR/SB = Spring rice/Autumn rice/Soybean S R / A R / W R N = Spring rice/Autumn rice/

Winter rice nursery S R N / A R / C = Spring rice nursery/Autumn rice/Corn P N / S P / V G •= Peanut/Sweet potato/Vegetables P N / C / V G = Peanut/Corn/Vegetables

6. Number of pigs this household kept 1 Last year (1991} | ] 2 1 year before (1990) [ | 3 2 years before (1989} [ J 4 3 years before (1988) [ ] 5 4 years before (1987) [ |

7. Reasons for the increase or decrease in number of pigs kept in a year

( 1

Appendix C i n

8. Total amount of pig manure produced last year tons [ ]

9. Use of pig manure produced last year 1 For spring crops tons [ ] 2 For autumn crops tons [ ] 3 For winter crops tons [ ] 4 tons [ ]

10. Does this household own or share buffalo or cattle? i (Yes ( )No [ ]

11. Total amount of buffalo or cattle manure produced last year tons [ ]

12. Use of buffalo or cattle manure last year 1 For spring crops tons | ] 2 For autumn crops tons [ ] 3 For winter crops tons [ ] 4 tons [ ]

13. Total amount of night soil produced last year tons [ ]

14. Use of night soil last year 1 For spring crops tons ( ] 2 For autumn crops tons | ) 3 For winter crops tons [ ] 4 tons [ I

15. Does the farmer think he has enough manure for his needs? ( } enough ( } not enough [ ]

16. If not enough, how much more manure would he like to have? tons [ ]

17. When the manure produced was not enough, what did the farmer do?

i i2 Soils Under Stress

Field Diagram Sheet

Use this sheet to draw a diagram of different fields and their relative distances from the house for use as a refer­ence when asking the farmer about crops grown in each field.

Appendix C 113

PART 2 (one for each field) FIELD DATA

Interviewer no Name

1. Household no Hamlet [ ]

2. Field no. of this household [ )

3. Area sao thuoc Convert to square meters = sq. m. [ ]

4. What field no. in the village field map is this field located? Map field no [ 1

5. Distance of this field from the house m. [ )

6. How long does it take to travel from the house to this field? minutes [ ]

7. Based on the cooperative classification, what is the land class of this field? Land class [ ]

8. Based on the general landscape topography of the village, this field is located in ( ) A relatively low spot ( ) A relatively high spot ( ) Somewhere in the middle [ ]

9. Does the farmer think this field has ( ) Good soil ( ) Poor soil ( ) Not so good but not so poor [ ) What are his reasons in judging whether the field has good or poor soil? | ]

10. How many crops were grown in this field in a year? [ ]

11. During the previous one-year cycle, starting with the spring crop (count rice nursery as one crop): What is the first crop grown? [ ( What is the second crop grown? [ ) What is the third crop grown? [ ) Other (if any) [ ]

i i4 Soils Under Stress

12. Draw lines in the table below, showing time from planting to harvesting of each crop in this field.

Month

Farmer's 12 1 2 3 4 5 6 7 8 9 i o n

Official's J F M A M J J A S O N D

13. How long has the above cropping pattern been grown in this field? years [ j

14. Had a different cropping pattern been used in this field in the past i o years? [ (Yes ( ) N o [ ]

15. If yes, what were the cropping patterns used in the past, and when were the changes made? Cropping pattern Year changed to a new one

i i

16. If there had been a change in cropping pattern in this field, what are the reasons?

1

FOR THE FIRST CROP GROWN LAST YEAR

17. What was the crop? | ]

18. What was the variety used? | ]

19. Was the crop grown on the entire field? ( ] Y e s ( ) N o | ] If no, area grown = sao thuoc [ ]

20. Amount of manure applied to this crop 1 Animal manure ( ) kg-total ( ) kg/sao [ ] 2 Night soil ( ) kg-total ( ) kg/sao [ ]

21. How was the manure transported to the field? 1 Animal manure by ( ] 2 Night soil by [ ]

Appendix C 115

22. Chemical fertilizers applied to this crop in this field 1 Nitrogen fertilizer: Kind [ |

Amount ( ) kg-total ( } kg/sao [ ]

2 Phosphorus fertilizer: Kind [ ] Amount ( } kg-total ( ] kg/sao | )

3 Potassium fertilizer: Kind [ ] Amount ( ) kg-total ( } kg/sao [ ]

4 Compound fertilizer: Kind ( ]

Amount ( ) kg-total ( } kg/sao [ ]

5 Lime: Amount ( | kg-total ( ) kg/sao [ )

6 Others (if any): Kind [ ] Amount ( ) kg-total ( ) kg/sao | ]

23. Was azolla applied to this crop in this field? ( )Yes ( ) N o [ ] If yes, amount applied ( ) kg-total ( ) kg/sao [ )

24. Was there any other kind of chemical fertilizer, manure, compost, or green manure applied to this crop in this field? If yes, kind [ ] Amount ( ) kg-total ( ) kg/sao [ )

25. What was the yield of this crop in this field last year? ( ) kg-tota! ( ) kg/sao [ )

26. During the past 10 years, what was the highest yield of this crop in this field?

( ) kg-total ( ) kg/sao [ ]

27. Why was high yield obtained in that year?

28. During the past 10 years, what was the lowest yield of this crop in this field?

( ) kg-total ( ) kg/sao

29. Why was low yield obtained in that year?

i 1

n 6 Soils Under Stress

FOR THE SECOND CROP GROWN LAST YEAR

30. What is the crop? [ |

31. What was the variety used? [ ]

32. Was the crop grown on the entire field? ( )Yes ( ) N o [ ] If no, area grown = sao thuoc \ \

33. Amount of manure applied to this crop 1 Animal manure [ ) kg-total ( ) kg/sao [ ] 2 Night soil ( ) kg-total ( ) kg/sao [ ]

34. How was the manure transported to the field? 1 Animal manure by [ ] 2 Night soil by [ ]

35. Chemical fertilizers applied to this crop in this field

1 Nitrogen fertilizer: Kind [ ] Amount ( ) kg-total ( ) kg/sao [ ]

2 Phosphorus fertilizer: Kind [ ] Amount ( ) kg-total ( ) kg/sao ( ]

3 Potassium fertilizer: Kind [ ] Amount ( } kg-total ( ) kg/sao [ ]

4 Compound fertilizer: Kind [ ]

Amount { ] kg-total ( ) kg/sao [ )

5 Lime: Amount ( ) kg-total | } kg/sao [ ]

6 Others (if any): Kind [ ] Amount ( ) kg-total ( ) kg/sao | ]

36. Was azolla applied to this crop in this field? ( ) Yes ( ) N o [ ] If yes, amount applied ( ) kg-total ( ) kg/sao [ ]

37. Was there any other kind of chemical fertilizer, manure, compost, or green manure applied to this crop in this field? If yes, kind I | Amount ( ) kg-total ( ) kg/sao [ ]

Appendix C 117

38. What was the yield of this crop in this field last year? I ) kg-total ( | kg/sao [

39. During the past 10 years, what was the highest yield of this crop in this field?

( ) kg-total ( ) kg/sao [

40. Why was high yield obtained in that year?

i

41. During the past 10 years, what was the lowest yield of this crop in this field?

( ) kg-total | ) kg/sao [

42. Why was low yield obtained in that year?

FOR THE THIRD CROP GROWN LAST YEAR

43. What is the crop?

44. What was the variety used?

45. Was the crop grown on the entire field? ( )Yes ( ) No ( If no, area grown = sao thuoc [

46. Amount of manure applied to this crop 1 Animal manure ( ) kg-total | ) kg/sao \ 2 Night soil ( | kg-total ( ) kg/sao \

47. How was the manure transported to the field? 1 Animal manure by [ 2 Night soil by 1

48. Chemical fertilizers applied to this crop in this field

T Nitrogen fertilizer: Kind [ Amount ( | kg-total ( ) kg/sao [

2 Phosphorus fertilizer: Kind | Amount ( ) kg-total ( ) kg/sao (

3 Potassium fertilizer: Kind [ Amount ( ) kg-total ( ) kg/sao \

n 8 Soils Under Stress

4 Compound fertilizer: Kind [ )

Amount ( ) kg-total ( ) kg/sao ( ]

5 Lime: Amount [ ) kg-total ( | kg/sao [ ]

6 Others |if any): Kind [ ] Amount ( ) kg-total ( ) kg/sao [ ]

49. Was azolla applied to this crop in this field? ( )Yes ( (No [ ] If yes, amount applied ( ) kg-total ( ) kg/sao [ ]

50. Was there any other kind of chemical fertilizer, manure, compost, or green manure applied to this crop in this field? If yes, kind | ) Amount ( ) kg-total ( ) kg/sao [ )

51. What was the yield of this crop in this field last year? ( ) kg-total ( ) kg/sao [ )

52. During the past 10 years, what was the highest yield of this crop in this field?

( ) kg-total ( ) kg/sao [ ]

53. Why was high yield obtained in that year?

: ! i

54. During the past 10 years, what was the lowest yield of this crop in this field?

( ) kg-total ( ) kg/sao [ ]

55. Why was low yield obtained in that year?

[ i

56. In the farmer's opinion, what are the problems of crop production in this field?

57. If the farmer wants to improve crop production in this field, what w i l l he do?

Angladette, Andre. 1966. L e r i z . Paris: G-P. Maisonneuve et Larose.

Conway, Gordon R. 1984.What is an agroecosystem and why is it worthy of study? In A n introduction to h u m a n ecology research on a g r i c u l t u r a l systems i n Southeast Asia, ed. A. Terry Rambo and Percy E. Sajise, 15-38. College, Laguna: University of the Philippines at Los Banos.

Godwin, D. C , U. Singh, R. J. Buresh, and S. K. De Datta. 1990. Modeling of nitrogen dynamics in relation to rice growth and yield. Vol. 4, Trans. 14th I n t . Congress Soil Science, 310-25. Kyoto, Japan.

Gourou, Pierre. 1936. Les paysans du D e l t a Tbnkinois (Peasants of the Tonkin Delta). Paris: l'Ecole Francaise d'Extreme-Orient. (Reprinted by Mouton, Paris, 1965-)

Jones, J. W. 1993. Decision support systems for agricultural development. In Systems approaches for a g r i c u l t u r a l development, ed. F. P. de Vries, P. Teng, and K. Metselaar. Dordrecht: Kluwer Academic Publishers.

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Le Trong Cue and A. Terry Rambo, eds. 1993- Too many people, too l i t t l e land: T h e h u m a n ecology of a wet rice-growing village i n the Red River D e l t a of V i e t n a m . Program on Environment Occasional Paper No. 15. Honolulu: East-West Center.

Le Trong Cue, A. T. Rambo, K. Fahrney, T. D. Vien, J. Romm, D. T. Sy, eds. 1996. Red books, green h i l l s : T h e impact of economic r e f o r m on restoration ecology i n the M i d l a n d s of n o r t h e r n V i e t n a m . Research Report. Honolulu: East-West Center, Program on Environment.

Le Trong Cue and Tran Due Vieh. 1993. An overview of the Red River Delta environment. In Too many people, too l i t t l e land: T h e h u m a n ecology of a wet rice-growing village i n the Red River D e l t a of V i e t n a m , ed. Le Trong Cue and A. Terry Rambo,. 1-10. Program on Environment Occasional Paper No. 15. Honolulu: East-West Center.

Luong, Hy V. 1992. Revolution i n the village: T r a d i t i o n and t r a n s f o r m a ­tion i n north V i e t n a m , r o 2 $ - i 9 8 8 . Honolulu: University of Hawaii Press.

Multiple Cropping Project. 1980. An interdisciplinary perspective of cropping systems in the Chiang Mai Valley: Key questions for research. Faculty of Agriculture, University of Chiang Mai, Thailand.

n o Soils Under Stress

Patanothai, Aran, Tran Due Vien, Le Thanh Tarn, and Phan Minh Nguyet. 1993. Sustainability: Nutrient flows and soils. In Too many people, too l i t t l e land: T h e h u m a n ecology of a wet rice-growing village i n the Red River D e l t a of V i e t n a m , ed. Le Trong Cue and A. Terry Rambo, 147-^4. Program on Environment Occasional Paper No. 15. Honolulu: East-West Center.

Rambo, A. Terry. 1983. Conceptual approaches to h u m a n ecology. Environment and Policy Institute Research Report No. T4. Honolulu: East-West Center.

Rambo, A. Terry. 1995. The composite swiddening system of the Tay ethnic minority of the northwestern mountains of Vietnam. Paper presented at the Regional Symposium on Montane Mainland Southeast Asia in Transition, Chiang Mai University, 12-17 November, Chiang Mai, Thailand. Forthcoming in symposium proceedings.

Rambo, A. Terry, Robert R. Reed, Le Trong Cue, and Michael DiGregorio, eds. 1995. T h e challenges of h i g h l a n d development i n V i e t n a m . Honolulu: East-West Center, Program on Environment.